/* ===========================================
   Discrete Math Speedrun
   Professional. Solid colors. No gradients.
   =========================================== */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&display=swap');

:root {
  --orange: #C2410C;            /* primary: passes WCAG AA on white & on orange-pale */
  --orange-strong: #C2410C;     /* filled bg with white text: 5.2 contrast */
  --orange-hover: #9A330A;      /* darker for button hover */
  --orange-pale: #FFF7ED;
  --orange-soft: #FFEDD5;
  --orange-line: #FED7AA;
  --green: #15803D;             /* darker green for AA contrast on green-pale */
  --green-strong: #15803D;
  --green-pale: #F0FDF4;
  --red: #B91C1C;               /* darker red for AA contrast on red-pale */
  --red-pale: #FEF2F2;
  /* Additional accent colours for typed callouts and chips */
  --blue: #1D4ED8;
  --blue-pale: #EFF6FF;
  --amber: #92400E;
  --amber-pale: #FFFBEB;
  --purple: #6D28D9;
  --purple-pale: #F5F3FF;

  --text: #111827;
  --text-soft: #374151;
  --text-mute: #5B6371;       /* slightly darkened so it passes AA on warm alt bg */
  --text-faint: #8A8E97;

  --bg: #FFFBF7;              /* subtle warm off-white, rgb(255,251,247) */
  --bg-alt: #FAF3E8;          /* slightly darker warm tint for stripes/alt rows */
  --bg-sidenav: #FFFBF7;

  --border: #EFE6D8;
  --border-strong: #D9CDB9;
  --code-bg: #FAF3E8;

  --shadow-sm: 0 1px 2px rgba(0,0,0,0.04);
  --shadow: 0 1px 3px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
  --shadow-md: 0 4px 12px -2px rgba(0,0,0,0.08), 0 2px 4px -1px rgba(0,0,0,0.04);

  --radius: 12px;
  --radius-lg: 14px;
  --radius-sm: 8px;
  --radius-pill: 999px;

  --sidenav-w: 240px;
  --font: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}

[data-theme="dark"] {
  --orange: #FB923C;            /* accent / text on dark bg */
  --orange-strong: #EA580C;     /* filled bg with white text — visible on dark, white passes AA large */
  --orange-hover: #FDBA74;
  --orange-pale: #261B12;       /* dark warm tint for callouts */
  --orange-soft: #382616;       /* slightly lighter for hovers */
  --orange-line: #4A331D;
  --green: #4ADE80;
  --green-strong: #15803D;      /* darker green so white text passes contrast */
  --green-pale: #131F18;
  --red: #F87171;
  --red-pale: #251416;
  --blue: #60A5FA;
  --blue-pale: #121C2C;
  --amber: #FBBF24;
  --amber-pale: #1F1808;
  --purple: #A78BFA;
  --purple-pale: #1B142A;

  --text: #ECEDF1;
  --text-soft: #C7CAD2;
  --text-mute: #8B8F9A;
  --text-faint: #5F6371;

  --bg: #101116;                /* requested near-black, rgb(16,17,22) */
  --bg-alt: #191A21;
  --bg-sidenav: #0B0C10;

  --border: #262830;
  --border-strong: #383B45;
  --code-bg: #191A21;

  --shadow-sm: 0 1px 2px rgba(0,0,0,0.4);
  --shadow: 0 1px 3px rgba(0,0,0,0.4), 0 1px 2px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 12px -2px rgba(0,0,0,0.5), 0 2px 4px -1px rgba(0,0,0,0.3);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--font);
  color: var(--text);
  background: var(--bg);
  line-height: 1.65;
  font-size: 15.5px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-feature-settings: "cv02", "cv03", "cv04", "cv11";
}

/* === Sidebar navigation === */
.sidenav {
  position: fixed;
  top: 0; left: 0; bottom: 0;
  width: var(--sidenav-w);
  background: var(--bg-sidenav);
  border-right: 1px solid var(--border);
  padding: 24px 16px 18px;
  display: flex;
  flex-direction: column;
  gap: 4px;
  overflow-y: auto;
  z-index: 100;
  transition: transform .25s ease;
}

.sidenav .brand {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--text);
  font-weight: 600;
  font-size: 15px;
  padding: 4px 8px 20px;
  margin-bottom: 8px;
  border-bottom: 1px solid var(--border);
  letter-spacing: -0.01em;
}
.brand-logo {
  width: 34px; height: 34px;
  border-radius: 8px;
  background: var(--orange-strong);
  display: grid; place-items: center;
  color: #fff;
  font-weight: 700;
  font-size: 13px;
  flex-shrink: 0;
  letter-spacing: 0;
}
.brand-text { line-height: 1.2; font-size: 14.5px; }

.sidenav-links {
  display: flex;
  flex-direction: column;
  gap: 1px;
  margin-top: 4px;
}
.sidenav-section {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-mute);
  padding: 14px 12px 8px;
  font-weight: 600;
}
.sidenav-links a {
  color: var(--text-soft);
  text-decoration: none;
  padding: 8px 12px;
  border-radius: var(--radius-sm);
  font-size: 13.5px;
  font-weight: 500;
  transition: background-color .12s, color .12s;
  display: flex;
  align-items: center;
}
.sidenav-links a:hover {
  background: var(--bg-alt);
  color: var(--text);
}
.sidenav-links a.active {
  background: var(--orange-pale);
  color: var(--orange);
  font-weight: 600;
}
[data-theme="dark"] .sidenav-links a.active {
  background: var(--orange-soft);
  color: var(--orange);
}

.sidenav-footer {
  margin-top: auto;
  padding-top: 14px;
  border-top: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.theme-toggle {
  width: 100%;
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 8px 12px;
  background: transparent;
  color: var(--text-soft);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  font: inherit;
  font-size: 13px;
  font-weight: 500;
  transition: background-color .12s, border-color .12s;
  font-family: var(--font);
}
.theme-toggle:hover {
  background: var(--bg-alt);
  border-color: var(--border-strong);
}
.theme-toggle .theme-icon-light,
.theme-toggle .theme-icon-dark { font-size: 14px; line-height: 1; }
[data-theme="dark"] .theme-toggle .theme-icon-light { display: inline; }
[data-theme="dark"] .theme-toggle .theme-icon-dark { display: none; }
[data-theme="dark"] .theme-toggle .theme-label-light { display: inline; }
[data-theme="dark"] .theme-toggle .theme-label-dark { display: none; }
.theme-toggle .theme-icon-light { display: none; }
.theme-toggle .theme-icon-dark { display: inline; }
.theme-toggle .theme-label-light { display: none; }
.theme-toggle .theme-label-dark { display: inline; }

/* === Mobile bar === */
.mobile-bar {
  display: none;
  position: sticky;
  top: 0;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  padding: 10px 16px;
  align-items: center;
  gap: 12px;
  z-index: 50;
}
.mobile-bar button {
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 6px 12px;
  cursor: pointer;
  color: var(--text);
  font: inherit;
  font-size: 16px;
}
.sidenav-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.35);
  z-index: 90;
}

@media (max-width: 900px) {
  .sidenav { transform: translateX(-100%); box-shadow: var(--shadow-md); }
  .sidenav.open { transform: translateX(0); }
  .sidenav-overlay.open { display: block; }
  .mobile-bar { display: flex; }
  .page-content { margin-left: 0 !important; }
}

/* === Page content === */
.page-content {
  margin-left: var(--sidenav-w);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* === Hero === */
.hero {
  background: var(--bg);
  border-bottom: 1px solid var(--border);
}
.hero-inner {
  max-width: 1080px;
  margin: 0 auto;
  padding: 64px 40px 48px;
}
.hero h1 {
  font-size: 38px;
  margin: 0 0 14px;
  line-height: 1.15;
  letter-spacing: -0.025em;
  color: var(--text);
  font-weight: 700;
}
.hero h1 .accent { color: var(--orange); }
.hero p.lede {
  font-size: 17px;
  color: var(--text-soft);
  max-width: 720px;
  margin: 0;
  line-height: 1.6;
}

/* === Progress widget === */
.progress-widget {
  display: flex;
  align-items: center;
  gap: 16px;
  margin: 28px 0 0;
  padding: 14px 18px;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  flex-wrap: wrap;
}
.progress-label {
  font-size: 13.5px;
  font-weight: 600;
  color: var(--text);
  display: flex;
  align-items: center;
  gap: 8px;
}
.progress-count { color: var(--orange); font-weight: 700; }
.progress-track {
  flex: 1;
  height: 6px;
  background: var(--bg-alt);
  border-radius: var(--radius-pill);
  overflow: hidden;
  min-width: 160px;
  border: 1px solid var(--border);
}
.progress-fill {
  height: 100%;
  background: var(--orange);
  border-radius: var(--radius-pill);
  width: 0%;
  transition: width .4s ease;
}
.streak-chip {
  font-size: 12px;
  font-weight: 600;
  background: var(--orange-pale);
  color: var(--orange);
  padding: 4px 10px;
  border-radius: var(--radius-pill);
  border: 1px solid var(--orange-line);
}
.streak-chip.hidden { display: none; }

.completion-banner {
  display: none;
  margin: 16px 0;
  padding: 14px 18px;
  background: var(--green-pale);
  color: var(--green);
  border: 1px solid var(--green);
  border-radius: var(--radius);
  font-weight: 600;
  font-size: 14.5px;
  text-align: center;
}
.completion-banner.show { display: block; }
[data-theme="dark"] .completion-banner { color: #86EFAC; }

/* === Main === */
main {
  max-width: 1080px;
  margin: 0 auto;
  padding: 40px 40px 80px;
  width: 100%;
  flex: 1;
}

/* === Layout with TOC === */
.layout {
  display: grid;
  grid-template-columns: 1fr 220px;
  gap: 40px;
  align-items: start;
}
.layout > div:first-child { min-width: 0; }
.layout .sidebar {
  position: sticky;
  top: 24px;
  order: 2;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  background: var(--bg);
  font-size: 13px;
  max-height: calc(100vh - 48px);
  overflow-y: auto;
}
.layout .sidebar h4 {
  margin: 0 0 10px;
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-mute);
  font-weight: 600;
}
.layout .sidebar a {
  display: block;
  padding: 5px 10px;
  margin: 1px 0;
  border-radius: 6px;
  color: var(--text-soft);
  text-decoration: none;
  font-size: 13px;
  font-weight: 500;
}
.layout .sidebar a:hover {
  background: var(--bg-alt);
  color: var(--text);
}
@media (max-width: 1100px) {
  .layout { grid-template-columns: 1fr; }
  .layout .sidebar { position: static; max-height: none; order: -1; margin-bottom: 12px; }
}

/* === Typography === */
h2 {
  font-size: 26px;
  margin: 44px 0 18px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
  color: var(--text);
  letter-spacing: -0.02em;
  font-weight: 700;
}
h2:first-child { margin-top: 0; }
h3 {
  font-size: 19px;
  margin: 28px 0 10px;
  color: var(--text);
  letter-spacing: -0.01em;
  font-weight: 600;
}
h4 {
  font-size: 16px;
  margin: 20px 0 8px;
  color: var(--text);
  font-weight: 600;
}
p { margin: 10px 0; }
ul, ol { margin: 10px 0; padding-left: 22px; }
li { margin: 4px 0; }
strong { color: var(--text); font-weight: 600; }
em { color: var(--text-soft); }

/* === Code === */
code, .mono {
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
  background: var(--code-bg);
  color: var(--orange);
  padding: 1.5px 6px;
  border-radius: 4px;
  font-size: 0.9em;
  border: 1px solid var(--border);
}
pre {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 14px 16px;
  overflow-x: auto;
  font-size: 13.5px;
  line-height: 1.55;
  color: var(--text);
}
pre code { background: transparent; padding: 0; color: var(--text); border: none; }

/* === Cards & callouts === */
.card {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 24px;
  margin: 18px 0;
}
.callout {
  border-left: 3px solid var(--orange);
  background: var(--orange-pale);
  padding: 14px 18px;
  border-radius: var(--radius-sm);
  margin: 16px 0;
}
.callout-title {
  font-weight: 600;
  color: var(--orange);
  margin: 0 0 6px;
  font-size: 12.5px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
}
.callout.tip { border-left-color: var(--green); background: var(--green-pale); }
.callout.tip .callout-title { color: var(--green); }
.callout.warn { border-left-color: var(--red); background: var(--red-pale); }
.callout.warn .callout-title { color: var(--red); }
.callout.def { border-left-color: var(--orange); background: var(--orange-pale); }

/* === Definition box === */
.defbox {
  background: var(--bg);
  border: 1px solid var(--border);
  border-left: 3px solid var(--orange);
  border-radius: var(--radius-sm);
  padding: 16px 20px;
  margin: 16px 0;
  color: var(--text);
}
.defbox-label {
  display: inline-block;
  background: var(--orange-strong);
  color: #fff;
  font-size: 10.5px;
  font-weight: 600;
  padding: 2px 9px;
  border-radius: var(--radius-pill);
  letter-spacing: 0.04em;
  margin-bottom: 10px;
  text-transform: uppercase;
}

/* === Tables === */
table {
  border-collapse: separate;
  border-spacing: 0;
  width: 100%;
  margin: 16px 0;
  font-size: 14px;
  color: var(--text);
  border-radius: var(--radius-sm);
  overflow: hidden;
  border: 1px solid var(--border);
}
th, td {
  border-bottom: 1px solid var(--border);
  padding: 10px 14px;
  text-align: center;
  line-height: 1.45;
}
th + th, td + td { border-left: 1px solid var(--border); }
tr:last-child td { border-bottom: none; }
th {
  background: var(--bg-alt);
  color: var(--text);
  font-weight: 600;
  font-size: 13px;
}
tbody tr:nth-child(even) td { background: var(--bg-alt); }
table.tt td.t { color: var(--green); font-weight: 600; }
table.tt td.f { color: var(--red); font-weight: 600; }

/* === Problem cards (Q&A) === */
.qcard {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 24px;
  margin: 18px 0;
  transition: border-color .15s;
}
.qcard:hover { border-color: var(--border-strong); }
.qcard.solved {
  border-color: var(--green);
}
.qcard.solved::before {
  content: "";
  display: block;
  position: absolute;
}
.qcard .qhead {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 10px;
  flex-wrap: wrap;
}
.qcard .qno {
  display: inline-block;
  background: var(--orange-strong);
  color: #fff;
  font-weight: 600;
  font-size: 11.5px;
  padding: 3px 10px;
  border-radius: var(--radius-pill);
  letter-spacing: 0.02em;
}
.qcard.solved .qno { background: var(--green-strong); }
.qcard .qtag {
  font-size: 11px;
  color: var(--text-mute);
  background: var(--bg-alt);
  border: 1px solid var(--border);
  padding: 2px 9px;
  border-radius: var(--radius-pill);
  font-weight: 500;
}
.qcard .solved-badge {
  margin-left: auto;
  font-size: 12px;
  color: var(--green);
  font-weight: 600;
  display: none;
}
.qcard.solved .solved-badge { display: inline-flex; align-items: center; gap: 4px; }
.qcard .question { margin: 6px 0 14px; }
.qcard .solution {
  border-top: 1px solid var(--border);
  padding-top: 14px;
  margin-top: 14px;
}
.qcard details > summary {
  cursor: pointer;
  color: var(--orange);
  font-weight: 600;
  list-style: none;
  user-select: none;
  padding: 7px 14px;
  background: var(--bg);
  border: 1px solid var(--orange);
  border-radius: var(--radius-sm);
  font-size: 13.5px;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  transition: background-color .12s, color .12s;
  font-family: var(--font);
}
.qcard details > summary::before {
  content: "▸";
  display: inline-block;
  transition: transform .15s ease;
  font-size: 10px;
}
.qcard details[open] > summary::before { transform: rotate(90deg); }
.qcard details > summary::after { content: "Show solution"; }
.qcard details[open] > summary::after { content: "Hide solution"; }
.qcard details > summary:hover {
  background: var(--orange-pale);
}
.qcard details[open] > summary { margin-bottom: 14px; }
.qcard details > summary::-webkit-details-marker { display: none; }

/* === Tags === */
.tag {
  display: inline-block;
  font-size: 11.5px;
  padding: 3px 10px;
  border-radius: var(--radius-pill);
  background: var(--bg-alt);
  color: var(--text-soft);
  border: 1px solid var(--border);
  margin-right: 6px;
  font-weight: 500;
}

/* === Topic grid === */
.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 16px;
  margin: 24px 0;
}
.topic-card {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px;
  text-decoration: none;
  color: var(--text);
  transition: border-color .15s, box-shadow .15s;
  display: flex;
  flex-direction: column;
  gap: 10px;
}
.topic-card:hover {
  border-color: var(--orange);
  box-shadow: var(--shadow-md);
}
.topic-card .num {
  display: inline-flex;
  width: 32px; height: 32px;
  background: var(--orange-pale);
  color: var(--orange);
  border: 1px solid var(--orange-line);
  border-radius: 8px;
  font-weight: 600;
  align-items: center; justify-content: center;
  font-size: 13px;
}
.topic-card h3 {
  margin: 6px 0 4px;
  color: var(--text);
  font-size: 17px;
  font-weight: 600;
}
.topic-card p {
  color: var(--text-soft);
  font-size: 14px;
  margin: 0;
  line-height: 1.55;
}
.topic-card .meta {
  margin-top: auto;
  padding-top: 14px;
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

/* === KaTeX === */
.katex { font-size: 1.02em !important; }
.katex-display { margin: 14px 0 !important; overflow-x: auto; overflow-y: hidden; }
[data-theme="dark"] .katex { color: var(--text); }

/* === Footer === */
footer {
  border-top: 1px solid var(--border);
  background: var(--bg);
  padding: 28px;
  text-align: center;
  color: var(--text-mute);
  font-size: 13px;
}

/* === Misc === */
hr {
  border: 0;
  border-top: 1px solid var(--border);
  margin: 32px 0;
}
a { color: var(--orange); text-decoration: none; }
a:hover { color: var(--orange-hover); text-decoration: underline; }
[data-theme="dark"] a:hover { color: var(--orange-hover); }
/* No underline on navigation links */
.sidenav a:hover,
.sidenav .brand:hover,
.layout .sidebar a:hover,
.toc a:hover,
.topic-card:hover { text-decoration: none; }

.flex-row { display: flex; gap: 12px; flex-wrap: wrap; align-items: center; }
.two-col { display: grid; grid-template-columns: 1fr 1fr; gap: 18px; }
@media (max-width: 800px) { .two-col { grid-template-columns: 1fr; } }

.badge {
  display: inline-block;
  padding: 2px 9px;
  background: var(--orange-strong);
  color: #fff;
  font-size: 11px;
  font-weight: 600;
  border-radius: var(--radius-pill);
  margin-left: 6px;
  letter-spacing: 0.02em;
}

.toc {
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px 22px;
  margin: 18px 0 28px;
}
.toc h4 { margin-top: 0; color: var(--text); font-size: 13px; text-transform: uppercase; letter-spacing: 0.06em; font-weight: 600; color: var(--text-mute); }
.toc ul { columns: 2; padding-left: 18px; }
@media (max-width: 700px) { .toc ul { columns: 1; } }
.toc a { color: var(--text-soft); text-decoration: none; font-weight: 500; }
.toc a:hover { color: var(--orange); }

.section-intro {
  font-size: 16px;
  color: var(--text-soft);
  max-width: 780px;
  line-height: 1.65;
}

.proof-tag {
  display: inline-block;
  background: var(--orange-pale);
  color: var(--orange);
  padding: 2px 8px;
  border-radius: 4px;
  font-size: 11.5px;
  font-weight: 600;
  margin-right: 6px;
  border: 1px solid var(--orange-line);
}

ul.checks { list-style: none; padding-left: 0; }
ul.checks li::before { content: "✓ "; color: var(--orange); font-weight: 700; margin-right: 4px; }

.kv { display: grid; grid-template-columns: max-content 1fr; gap: 4px 16px; margin: 10px 0; }
.kv dt { color: var(--text-mute); font-size: 13.5px; }
.kv dd { margin: 0; font-weight: 500; }

.steps { counter-reset: step; list-style: none; padding-left: 0; }
.steps > li {
  counter-increment: step;
  padding: 6px 0 6px 40px;
  position: relative;
  margin: 4px 0;
}
.steps > li::before {
  content: counter(step);
  position: absolute;
  left: 0; top: 7px;
  width: 26px; height: 26px;
  background: var(--bg);
  border: 1.5px solid var(--orange);
  color: var(--orange);
  border-radius: 50%;
  font-weight: 600;
  display: grid; place-items: center;
  font-size: 12px;
}

.formula {
  background: var(--orange-pale);
  border-left: 3px solid var(--orange);
  padding: 12px 18px;
  margin: 12px 0;
  border-radius: var(--radius-sm);
  font-size: 16px;
  color: var(--text);
}

/* CTA buttons */
.btn-primary {
  background: var(--orange-strong) !important;
  color: #fff !important;
  text-decoration: none;
  padding: 10px 22px;
  border-radius: var(--radius-sm);
  font-weight: 600;
  display: inline-block;
  transition: background-color .12s;
  font-size: 14px;
}
.btn-primary:hover { background: #9A330A !important; text-decoration: none; }
[data-theme="dark"] .btn-primary:hover { background: #C2410C !important; }
.btn-secondary {
  background: var(--bg) !important;
  color: var(--text) !important;
  text-decoration: none;
  padding: 10px 22px;
  border-radius: var(--radius-sm);
  font-weight: 600;
  border: 1px solid var(--border-strong);
  display: inline-block;
  transition: border-color .12s, background-color .12s;
  font-size: 14px;
}
.btn-secondary:hover { border-color: var(--orange); background: var(--orange-pale) !important; text-decoration: none; }

/* Solved indicator (floats up briefly when revealing) */
.flash-plus {
  position: fixed;
  color: var(--green);
  font-weight: 600;
  font-size: 14px;
  pointer-events: none;
  z-index: 9999;
  animation: float-up 1s ease-out forwards;
}
@keyframes float-up {
  0% { opacity: 0; transform: translateY(0) scale(0.9); }
  20% { opacity: 1; }
  100% { opacity: 0; transform: translateY(-40px) scale(1); }
}

/* ===========================================
   NEW COMPONENTS (design pass)
   =========================================== */

/* --- Topic breadcrumb chip (above hero h1) --- */
.topic-chip {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 12px;
  background: var(--orange-pale);
  border: 1px solid var(--orange-line);
  color: var(--orange);
  font-size: 11.5px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  border-radius: var(--radius-pill);
  margin-bottom: 14px;
}

/* --- Meta row (below lede) --- */
.meta-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px;
  margin-top: 14px;
  font-size: 13px;
  color: var(--text-mute);
  font-weight: 500;
}
.meta-row > span { display: inline-flex; align-items: center; gap: 6px; }
.meta-row .sep {
  width: 4px; height: 4px;
  background: var(--text-faint);
  border-radius: 50%;
  display: inline-block;
}

/* --- Sidenav section: add icon + visual divider between groups --- */
.sidenav-section + .sidenav-links { margin-bottom: 6px; }

/* --- New callout variants: example, analogy, key, note --- */
.callout.example { border-left-color: var(--amber); background: var(--amber-pale); }
.callout.example .callout-title { color: var(--amber); }
.callout.analogy { border-left-color: var(--blue); background: var(--blue-pale); }
.callout.analogy .callout-title { color: var(--blue); }
.callout.key { border-left-color: var(--orange); background: var(--orange-pale); }
.callout.key .callout-title { color: var(--orange); }
.callout.note { border-left-color: var(--text-mute); background: var(--bg-alt); }
.callout.note .callout-title { color: var(--text-mute); }
/* Adjust dark mode body text colour on callouts so paragraphs stay readable */
[data-theme="dark"] .callout.example,
[data-theme="dark"] .callout.analogy,
[data-theme="dark"] .callout.note,
[data-theme="dark"] .callout.key { color: var(--text); }

/* Optional leading icon on callouts via data-icon attribute */
.callout[data-icon] .callout-title::before {
  content: attr(data-icon) " ";
  margin-right: 4px;
}

/* --- Key Takeaways block (end-of-topic) --- */
.takeaways {
  margin: 32px 0 0;
  background: var(--bg);
  border: 1px solid var(--orange-line);
  border-radius: var(--radius-lg);
  overflow: hidden;
}
.takeaways-head {
  background: var(--orange);
  color: #fff;
  font-weight: 700;
  padding: 10px 20px;
  font-size: 14px;
  letter-spacing: 0.02em;
  display: flex;
  align-items: center;
  gap: 8px;
}
.takeaways-head::before { content: "🎯"; font-size: 16px; }
.takeaways-body { padding: 18px 24px 22px; }
.takeaways ul { margin: 0; padding-left: 20px; }
.takeaways li { margin: 6px 0; }
[data-theme="dark"] .takeaways-head { background: var(--orange-strong); }

/* --- Previous / Next pager (bottom of topic) --- */
.pager {
  margin-top: 40px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
}
.pager a {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 14px 18px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  text-decoration: none;
  color: var(--text);
  background: var(--bg);
  transition: border-color .15s, box-shadow .15s;
}
.pager a:hover {
  border-color: var(--orange);
  text-decoration: none;
  box-shadow: var(--shadow);
}
.pager-prev { text-align: left; }
.pager-next { text-align: right; align-items: flex-end; }
.pager-label {
  font-size: 11.5px;
  color: var(--text-mute);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  font-weight: 600;
}
.pager-title { font-size: 15px; font-weight: 600; color: var(--text); }
.pager-spacer { /* used when one side is empty */ visibility: hidden; }
@media (max-width: 600px) {
  .pager { grid-template-columns: 1fr; }
  .pager-next { text-align: left; align-items: flex-start; }
}

/* --- Question type chip (qcards) --- */
.qtype {
  display: inline-block;
  font-size: 11px;
  font-weight: 700;
  padding: 3px 10px;
  border-radius: var(--radius-pill);
  letter-spacing: 0.04em;
  text-transform: uppercase;
  border: 1px solid transparent;
}
.qtype-proof { background: var(--purple-pale); color: var(--purple); border-color: var(--purple); border-color: color-mix(in srgb, var(--purple) 30%, transparent); }
.qtype-compute { background: var(--orange-pale); color: var(--orange); border-color: var(--orange-line); }
.qtype-translate { background: var(--blue-pale); color: var(--blue); border-color: color-mix(in srgb, var(--blue) 30%, transparent); }
.qtype-concept { background: var(--green-pale); color: var(--green); border-color: color-mix(in srgb, var(--green) 30%, transparent); }
/* Fallback for browsers without color-mix: solid translucent borders */
@supports not (color: color-mix(in srgb, red, blue)) {
  .qtype-proof    { border-color: var(--purple); }
  .qtype-translate{ border-color: var(--blue); }
  .qtype-concept  { border-color: var(--green); }
}

/* --- Stronger inline emphasis --- */
strong { color: var(--text); font-weight: 600; }
p strong, li strong { color: var(--text); }

/* --- Slightly tighten qcard head for the extra chip --- */
.qcard .qhead { gap: 8px; }

/* ===========================================
   PHASE 2 COMPONENTS
   =========================================== */

/* --- Skip to content (a11y) --- */
.skip-link {
  position: absolute;
  left: -9999px;
  top: 8px;
  padding: 8px 14px;
  background: var(--orange-strong);
  color: #fff;
  border-radius: 6px;
  z-index: 200;
  font-weight: 600;
  text-decoration: none;
}
.skip-link:focus {
  left: 16px;
  outline: 2px solid #fff;
  outline-offset: 2px;
}

/* Improved focus indicators */
a:focus-visible,
button:focus-visible,
[tabindex]:focus-visible,
input:focus-visible,
select:focus-visible,
summary:focus-visible {
  outline: 2px solid var(--orange);
  outline-offset: 2px;
  border-radius: 4px;
}

/* --- Search palette (Ctrl+K) --- */
.search-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.45);
  z-index: 500;
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding-top: 80px;
}
.search-overlay.open { display: flex; }
.search-modal {
  width: 100%;
  max-width: 560px;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: 0 24px 60px -12px rgba(0,0,0,0.4);
  max-height: 70vh;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}
.search-input-row {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 14px 18px;
  border-bottom: 1px solid var(--border);
}
.search-input-row svg { color: var(--text-mute); flex-shrink: 0; }
.search-input {
  flex: 1;
  border: none;
  background: transparent;
  font: inherit;
  font-size: 16px;
  outline: none;
  color: var(--text);
  font-family: var(--font);
}
.search-input::placeholder { color: var(--text-mute); }
.search-kbd-hint {
  font-size: 11px;
  color: var(--text-mute);
  font-family: ui-monospace, monospace;
  padding: 3px 7px;
  border: 1px solid var(--border-strong);
  border-radius: 4px;
  background: var(--bg-alt);
}
.search-results {
  overflow-y: auto;
  padding: 6px 0;
}
.search-group-title {
  padding: 10px 18px 4px;
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-mute);
  font-weight: 700;
}
.search-result {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 18px;
  text-decoration: none;
  color: var(--text);
  cursor: pointer;
  border-left: 3px solid transparent;
}
.search-result:hover,
.search-result.selected {
  background: var(--orange-pale);
  border-left-color: var(--orange);
  text-decoration: none;
}
.search-result-icon {
  font-size: 14px;
  color: var(--text-mute);
  width: 18px;
  text-align: center;
}
.search-result-title { font-weight: 500; flex: 1; font-size: 14px; }
.search-result-page {
  font-size: 11.5px;
  color: var(--text-mute);
  background: var(--bg-alt);
  padding: 2px 8px;
  border-radius: 999px;
}
.search-empty {
  padding: 30px 20px;
  text-align: center;
  color: var(--text-mute);
  font-size: 14px;
}

/* --- Glossary tooltip --- */
.glossary-term {
  position: relative;
  border-bottom: 1px dotted var(--orange);
  cursor: help;
}
.glossary-term:hover::after,
.glossary-term:focus::after {
  content: attr(data-def);
  position: absolute;
  bottom: calc(100% + 8px);
  left: 50%;
  transform: translateX(-50%);
  background: var(--text);
  color: var(--bg);
  padding: 8px 12px;
  border-radius: 6px;
  font-size: 12.5px;
  line-height: 1.45;
  font-weight: 500;
  white-space: normal;
  width: max-content;
  max-width: 280px;
  z-index: 50;
  box-shadow: 0 6px 14px -4px rgba(0,0,0,0.3);
  border-bottom: none;
  pointer-events: none;
}
.glossary-term:hover::before,
.glossary-term:focus::before {
  content: "";
  position: absolute;
  bottom: calc(100% + 3px);
  left: 50%;
  transform: translateX(-50%);
  border: 5px solid transparent;
  border-top-color: var(--text);
  z-index: 50;
  pointer-events: none;
}

/* --- Per-topic Quiz --- */
.quiz-block {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 0;
  margin: 28px 0;
  overflow: hidden;
}
.quiz-head {
  background: var(--bg-alt);
  border-bottom: 1px solid var(--border);
  padding: 14px 22px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}
.quiz-head h3 {
  margin: 0;
  font-size: 17px;
  color: var(--text);
  display: flex;
  align-items: center;
  gap: 8px;
}
.quiz-head h3::before {
  content: "✦";
  color: var(--orange);
}
.quiz-meta { font-size: 12.5px; color: var(--text-mute); }
.quiz-body { padding: 18px 22px 22px; }
.quiz-q {
  border-bottom: 1px dashed var(--border);
  padding: 14px 0;
}
.quiz-q:first-child { padding-top: 0; }
.quiz-q:last-child { border-bottom: none; padding-bottom: 0; }
.quiz-q-title {
  font-weight: 600;
  font-size: 15px;
  margin-bottom: 10px;
  color: var(--text);
}
.quiz-q-title .quiz-q-num {
  display: inline-block;
  background: var(--orange);
  color: #fff;
  font-size: 11px;
  font-weight: 700;
  padding: 2px 8px;
  border-radius: 999px;
  margin-right: 8px;
}
.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.quiz-option {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 9px 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  background: var(--bg);
  font-size: 14px;
  color: var(--text);
  transition: border-color .12s, background .12s;
}
.quiz-option:hover { border-color: var(--border-strong); background: var(--bg-alt); }
.quiz-option.selected {
  border-color: var(--orange);
  background: var(--orange-pale);
}
.quiz-option.correct {
  border-color: var(--green);
  background: var(--green-pale);
}
.quiz-option.incorrect {
  border-color: var(--red);
  background: var(--red-pale);
}
.quiz-option .quiz-letter {
  display: inline-flex;
  width: 22px; height: 22px;
  border: 1px solid var(--border-strong);
  border-radius: 50%;
  align-items: center;
  justify-content: center;
  font-size: 12px;
  font-weight: 700;
  color: var(--text-mute);
  flex-shrink: 0;
}
.quiz-option.selected .quiz-letter { background: var(--orange); color: #fff; border-color: var(--orange); }
.quiz-option.correct .quiz-letter { background: var(--green); color: #fff; border-color: var(--green); }
.quiz-option.incorrect .quiz-letter { background: var(--red); color: #fff; border-color: var(--red); }
.quiz-explain {
  margin-top: 10px;
  padding: 10px 14px;
  background: var(--bg-alt);
  border-left: 3px solid var(--green);
  border-radius: 0 6px 6px 0;
  font-size: 13.5px;
  color: var(--text-soft);
  display: none;
}
.quiz-explain.show { display: block; }
.quiz-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  margin-top: 16px;
  padding-top: 14px;
  border-top: 1px solid var(--border);
  flex-wrap: wrap;
}
.quiz-score {
  font-size: 14px;
  color: var(--text);
}
.quiz-score strong { color: var(--orange); }
.quiz-btn {
  background: var(--orange-strong);
  color: #fff;
  border: none;
  padding: 8px 18px;
  border-radius: var(--radius-sm);
  font-weight: 600;
  font-size: 13.5px;
  cursor: pointer;
  font-family: var(--font);
}
.quiz-btn:hover { background: var(--orange-hover); }
.quiz-btn.secondary {
  background: var(--bg);
  color: var(--text);
  border: 1px solid var(--border-strong);
}
.quiz-btn.secondary:hover { border-color: var(--orange); }

/* --- Interactive tool wrapper (truth table / K-map / mod arithmetic) --- */
.tool {
  background: var(--bg);
  border: 1px solid var(--orange-line);
  border-radius: var(--radius-lg);
  padding: 0;
  margin: 24px 0;
  overflow: hidden;
}
.tool-head {
  background: var(--orange-pale);
  border-bottom: 1px solid var(--orange-line);
  padding: 12px 20px;
  display: flex;
  align-items: center;
  gap: 8px;
  font-weight: 600;
  font-size: 14px;
  color: var(--orange);
}
.tool-head::before { content: "▣"; font-size: 14px; }
.tool-body { padding: 18px 22px 22px; }
.tool-row {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 12px;
  flex-wrap: wrap;
}
.tool-input {
  flex: 1;
  min-width: 200px;
  padding: 8px 12px;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  font-family: ui-monospace, monospace;
  font-size: 14px;
  background: var(--bg);
  color: var(--text);
}
.tool-input:focus {
  outline: 2px solid var(--orange);
  outline-offset: 0;
  border-color: var(--orange);
}
.tool-btn {
  background: var(--orange-strong);
  color: #fff;
  border: none;
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  font-weight: 600;
  font-size: 14px;
  cursor: pointer;
  font-family: var(--font);
}
.tool-btn:hover { background: var(--orange-hover); }
.tool-btn.alt {
  background: var(--bg);
  color: var(--text);
  border: 1px solid var(--border-strong);
}
.tool-btn.alt:hover { border-color: var(--orange); }
.tool-output {
  margin-top: 12px;
  font-size: 14px;
}
.tool-help {
  font-size: 12.5px;
  color: var(--text-mute);
  margin: 4px 0 0;
}
.tool-result {
  background: var(--bg-alt);
  border-radius: 8px;
  padding: 12px 16px;
  margin: 10px 0;
}
.tool-error {
  background: var(--red-pale);
  border-left: 3px solid var(--red);
  border-radius: 0 6px 6px 0;
  padding: 8px 14px;
  color: var(--red);
  font-size: 13.5px;
}
.tt-out table { font-size: 13.5px; }
.tt-out td.t { color: var(--green); font-weight: 700; }
.tt-out td.f { color: var(--red); font-weight: 700; }

/* K-map grid */
.kmap-grid {
  display: grid;
  grid-template-columns: auto repeat(4, 56px);
  gap: 4px;
  margin: 14px 0;
  font-family: ui-monospace, monospace;
  font-size: 13.5px;
}
.kmap-grid .kmap-label {
  background: transparent;
  padding: 8px 6px;
  font-weight: 600;
  color: var(--text-mute);
  text-align: center;
  border: none;
}
.kmap-grid .kmap-cell {
  width: 56px; height: 48px;
  background: var(--bg);
  border: 1.5px solid var(--border-strong);
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  font-weight: 700;
  font-size: 15px;
  color: var(--text);
  user-select: none;
}
.kmap-grid .kmap-cell:hover { border-color: var(--orange); }
.kmap-grid .kmap-cell.on {
  background: var(--orange);
  color: #fff;
  border-color: var(--orange);
}

/* --- Difficulty chip --- */
.diff {
  display: inline-block;
  font-size: 10.5px;
  font-weight: 700;
  letter-spacing: 0.04em;
  padding: 2px 8px;
  border-radius: 999px;
  border: 1px solid transparent;
  text-transform: uppercase;
}
.diff-easy   { color: var(--green); background: var(--green-pale); border-color: var(--green); }
.diff-medium { color: var(--amber); background: var(--amber-pale); border-color: var(--amber); }
.diff-hard   { color: var(--red);   background: var(--red-pale);   border-color: var(--red); }

/* --- Progress dashboard --- */
.dashboard {
  background: var(--bg);
  border: 1px solid var(--orange-line);
  border-radius: var(--radius-lg);
  padding: 0;
  margin: 24px 0 0;
  overflow: hidden;
}
.dashboard-head {
  background: var(--orange-pale);
  border-bottom: 1px solid var(--orange-line);
  padding: 12px 22px;
  font-weight: 600;
  font-size: 14px;
  color: var(--orange);
  display: flex;
  align-items: center;
  gap: 8px;
}
.dashboard-head::before { content: "📊"; }
.dashboard-body { padding: 18px 22px 20px; }
.dashboard-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 16px;
  margin-bottom: 16px;
}
.dashboard-stat {
  background: var(--bg-alt);
  border-radius: 10px;
  padding: 14px 16px;
  text-align: center;
}
.dashboard-stat-value {
  font-size: 28px;
  font-weight: 700;
  color: var(--orange);
  line-height: 1.1;
  font-feature-settings: "tnum";
}
.dashboard-stat-label {
  font-size: 12.5px;
  color: var(--text-mute);
  margin-top: 4px;
}
.dashboard-bar {
  height: 8px;
  background: var(--bg-alt);
  border-radius: 999px;
  overflow: hidden;
  margin: 6px 0;
}
.dashboard-bar-fill {
  height: 100%;
  background: var(--orange);
  width: 0%;
  transition: width .4s ease;
}
.dashboard-per-topic {
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.dashboard-per-topic-row {
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 13.5px;
}
.dashboard-per-topic-row a { flex: 0 0 120px; font-weight: 500; }
.dashboard-per-topic-row .dashboard-bar { flex: 1; margin: 0; }
.dashboard-per-topic-row .dashboard-pct {
  font-variant-numeric: tabular-nums;
  width: 40px;
  text-align: right;
  font-size: 12.5px;
  color: var(--text-mute);
}

/* --- Hero illustration --- */
.hero-illustration {
  position: absolute;
  right: 36px;
  bottom: 12px;
  width: 360px;
  height: 220px;
  pointer-events: none;
  opacity: 0.95;
}
@media (max-width: 900px) {
  .hero-illustration { display: none; }
}
.hero-illustration .float {
  animation: hero-float 7s ease-in-out infinite;
  transform-origin: center;
}
.hero-illustration .float-2 { animation-delay: -2s; }
.hero-illustration .float-3 { animation-delay: -4s; }
@keyframes hero-float {
  0%, 100% { transform: translateY(0px); }
  50% { transform: translateY(-6px); }
}

/* Hero-inner needs to host illustration */
.hero-inner { position: relative; }

/* Tweak hero-inner when illustration is present */
.hero.has-illustration .hero-inner { padding-right: 380px; }
@media (max-width: 1100px) {
  .hero.has-illustration .hero-inner { padding-right: 36px; }
}

/* ===========================================
   STICKY TOP BAR with search affordance
   =========================================== */
.topbar {
  position: sticky;
  top: 0;
  z-index: 60;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  padding: 10px 36px;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 12px;
  -webkit-backdrop-filter: saturate(180%) blur(10px);
  backdrop-filter: saturate(180%) blur(10px);
  /* Translucent so content scrolling underneath has a subtle frosted feel */
  background: color-mix(in srgb, var(--bg) 88%, transparent);
}
@supports not (background: color-mix(in srgb, red, blue)) {
  .topbar { background: var(--bg); }
}

.topbar-search {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 7px 12px;
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
  color: var(--text-mute);
  min-width: 320px;
  font-family: var(--font);
  font-size: 13.5px;
  font-weight: 500;
  transition: border-color .15s, background .15s, color .15s;
}
.topbar-search:hover {
  border-color: var(--orange);
  background: var(--bg);
  color: var(--text);
}
.topbar-search svg { flex-shrink: 0; opacity: 0.7; }
.topbar-search-text { flex: 1; text-align: left; }
.topbar-search-kbd {
  border: 1px solid var(--border-strong);
  border-radius: 4px;
  padding: 1px 7px;
  font-family: ui-monospace, monospace;
  font-size: 11px;
  color: var(--text-mute);
  background: var(--bg);
  white-space: nowrap;
}

/* On mobile: hide desktop topbar (mobile-bar gets a search button instead) */
@media (max-width: 900px) {
  .topbar { display: none; }
}

/* Mobile-bar search button */
.mobile-bar-search {
  margin-left: auto;
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 6px 10px;
  cursor: pointer;
  color: var(--text);
  font-size: 14px;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--font);
}
.mobile-bar-search:hover { border-color: var(--orange); }

/* ===========================================
   NEW TOOL COMPONENTS (Master Th. / Inference / Cayley / DH)
   =========================================== */

/* Inference trainer */
.inf-card { padding: 4px 0; }
.inf-meta { color: var(--text-mute); font-size: 12.5px; margin-bottom: 12px; }
.inf-label {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-mute);
  font-weight: 600;
  margin-bottom: 4px;
}
.inf-premises {
  background: var(--bg-alt);
  border-radius: 8px;
  padding: 10px 14px;
  margin-bottom: 10px;
}
.inf-premise { font-size: 14.5px; margin: 4px 0; color: var(--text); }
.inf-conclusion {
  background: var(--orange-pale);
  border-left: 3px solid var(--orange);
  border-radius: 0 8px 8px 0;
  padding: 10px 14px;
  margin-bottom: 14px;
}
.inf-concl-text { font-size: 15px; font-weight: 600; color: var(--text); }
.inf-question { font-weight: 600; margin: 12px 0 8px; color: var(--text); }
.inf-options {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 8px;
  margin-bottom: 14px;
}
.inf-option {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 2px;
  padding: 10px 14px;
  background: var(--bg);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  font: inherit;
  font-family: var(--font);
  text-align: left;
  transition: border-color .12s, background .12s;
}
.inf-option:hover { border-color: var(--orange); background: var(--orange-pale); }
.inf-option strong { font-size: 14px; color: var(--orange); }
.inf-option-name { font-size: 12px; color: var(--text-mute); }
.inf-option.correct { border-color: var(--green); background: var(--green-pale); }
.inf-option.correct strong { color: var(--green); }
.inf-option.incorrect { border-color: var(--red); background: var(--red-pale); }
.inf-option.incorrect strong { color: var(--red); }
.inf-explain {
  background: var(--bg-alt);
  border-left: 3px solid var(--green);
  border-radius: 0 8px 8px 0;
  padding: 10px 14px;
  font-size: 13.5px;
  color: var(--text-soft);
  margin-bottom: 12px;
}
.inf-actions { display: flex; gap: 8px; flex-wrap: wrap; }

/* Cayley table */
.cayley-wrap { overflow-x: auto; margin: 8px 0; }
.cayley {
  border-collapse: collapse;
  font-family: ui-monospace, monospace;
  font-size: 13.5px;
  margin: 0;
}
.cayley th, .cayley td {
  border: 1px solid var(--border);
  padding: 6px 10px;
  text-align: center;
  min-width: 36px;
  background: var(--bg);
  transition: background .12s;
}
.cayley thead th {
  background: var(--bg-alt);
  color: var(--orange);
  font-weight: 700;
}
.cayley tbody th {
  background: var(--bg-alt);
  color: var(--orange);
  font-weight: 700;
}
.cayley .cayley-corner { background: var(--orange-pale); color: var(--orange); }
.cayley td.identity { background: var(--orange-pale); color: var(--orange); font-weight: 700; }
.cayley td.hl-row, .cayley td.hl-col,
.cayley th.hl-row, .cayley th.hl-col {
  background: var(--orange-soft);
}
.cayley td.hl-row.hl-col {
  background: var(--orange);
  color: #fff;
}

/* Diffie–Hellman walkthrough */
.dh-grid {
  display: grid;
  grid-template-columns: 1fr 1.4fr 1fr;
  gap: 12px;
  margin: 8px 0 16px;
}
@media (max-width: 800px) {
  .dh-grid { grid-template-columns: 1fr; }
}
.dh-col {
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 12px 14px;
  font-size: 13.5px;
}
.dh-col.alice { border-top: 3px solid var(--blue); }
.dh-col.bob { border-top: 3px solid var(--green); }
.dh-col.channel { border-top: 3px solid var(--orange); }
.dh-head {
  font-weight: 700;
  margin-bottom: 8px;
  font-size: 14px;
}
.dh-row {
  padding: 6px 0;
  border-top: 1px dashed var(--border);
  color: var(--text);
}
.dh-row:first-of-type { border-top: none; }
.dh-row.dh-active {
  background: var(--orange-pale);
  border-radius: 6px;
  padding: 6px 10px;
  border-top: none;
  margin: 4px -6px;
}
.dh-row.dh-eve {
  background: var(--red-pale);
  border-radius: 6px;
  padding: 8px 10px;
  border-top: none;
  margin: 4px -6px;
  color: var(--text);
  font-size: 13px;
}
.dh-result {
  background: var(--green-pale);
  border-left: 3px solid var(--green);
  border-radius: 0 8px 8px 0;
  padding: 10px 14px;
  margin-bottom: 12px;
  font-size: 14.5px;
  color: var(--text);
}
.dh-controls {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  flex-wrap: wrap;
}

/* Master Theorem presets */
.mt-presets { display: flex; flex-wrap: wrap; gap: 6px; margin: 6px 0 12px; }
.mt-preset {
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 4px 12px;
  font-size: 12px;
  font-weight: 600;
  color: var(--text-soft);
  cursor: pointer;
  font-family: var(--font);
}
.mt-preset:hover { border-color: var(--orange); color: var(--orange); }