/* ============================================================
   SE375 Study Platform — Design System
   ============================================================ */

:root {
  --bg:           #0a0e1a;
  --bg2:          #0f1525;
  --card:         #111827;
  --card2:        #1a2235;
  --border:       #1f2d45;
  --border2:      #253350;

  --text:         #f1f5f9;
  --text2:        #cbd5e1;
  --muted:        #64748b;

  --orange:       #f97316;
  --orange-dim:   #c2530d;
  --orange-glow:  rgba(249,115,22,0.15);

  --blue:         #3b82f6;
  --blue-dim:     #1d4ed8;
  --blue-glow:    rgba(59,130,246,0.15);

  --green:        #10b981;
  --green-glow:   rgba(16,185,129,0.15);

  --red:          #ef4444;
  --red-glow:     rgba(239,68,68,0.15);

  --yellow:       #f59e0b;
  --yellow-glow:  rgba(245,158,11,0.15);

  --purple:       #8b5cf6;
  --purple-glow:  rgba(139,92,246,0.15);

  --radius:       12px;
  --radius-sm:    8px;
  --radius-lg:    18px;
  --shadow:       0 4px 24px rgba(0,0,0,0.4);
  --shadow-lg:    0 8px 40px rgba(0,0,0,0.5);

  --font:         'Inter', system-ui, -apple-system, sans-serif;
  --font-mono:    'JetBrains Mono', 'Fira Code', Consolas, monospace;
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--font);
  font-size: 15px;
  line-height: 1.65;
  min-height: 100vh;
}

/* ── Nav ────────────────────────────────────────────── */
.topnav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(10,14,26,0.95);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
}

.nav-inner {
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  gap: 8px;
  height: 60px;
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  flex-shrink: 0;
}

.brand-logo {
  flex-shrink: 0;
  filter: drop-shadow(0 0 6px rgba(249,115,22,0.35));
  transition: filter 0.2s;
}
.nav-brand:hover .brand-logo {
  filter: drop-shadow(0 0 10px rgba(249,115,22,0.6));
}

.brand-label {
  display: flex;
  flex-direction: column;
  gap: 1px;
}

.brand-name {
  font-size: 15px;
  font-weight: 800;
  color: var(--orange);
  letter-spacing: 0.03em;
  line-height: 1;
}

.brand-sub {
  font-size: 11px;
  font-weight: 500;
  color: var(--muted);
  white-space: nowrap;
  line-height: 1;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 2px;
  list-style: none;
  margin-left: auto;
}

.nav-link {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 7px 13px;
  border-radius: var(--radius-sm);
  text-decoration: none;
  color: var(--text2);
  font-size: 13.5px;
  font-weight: 500;
  transition: background 0.15s, color 0.15s;
  white-space: nowrap;
}

.nav-link:hover { background: var(--card2); color: var(--text); }
.nav-link.active { background: var(--orange-glow); color: var(--orange); }
.nav-link.nav-quiz { color: var(--yellow); }
.nav-link.nav-quiz.active { background: var(--yellow-glow); }
.nav-link.nav-quiz:hover { background: var(--yellow-glow); color: var(--yellow); }
.nav-link.nav-analysis { color: var(--blue); }
.nav-link.nav-analysis.active { background: var(--blue-glow); color: var(--blue); }
.nav-link.nav-analysis:hover { background: var(--blue-glow); color: var(--blue); }
.nav-link.nav-slides { color: #a78bfa; }
.nav-link.nav-slides.active { background: rgba(167,139,250,.12); color: #a78bfa; }
.nav-link.nav-slides:hover { background: rgba(167,139,250,.12); color: #a78bfa; }

.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--text);
  font-size: 22px;
  cursor: pointer;
  margin-left: auto;
  padding: 4px 8px;
}

/* ── Language Switcher ───────────────────────────────── */
.lang-switch {
  display: flex;
  align-items: center;
  gap: 2px;
  margin-left: 8px;
  border-left: 1px solid var(--border);
  padding-left: 10px;
  flex-shrink: 0;
}
.lang-btn {
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.06em;
  color: var(--text2);
  text-decoration: none;
  transition: background 0.15s, color 0.15s;
}
.lang-btn:hover { background: var(--card2); color: var(--text); }
.lang-btn.lang-active {
  background: var(--orange-glow);
  color: var(--orange);
}

/* ── Layout ─────────────────────────────────────────── */
.main-content {
  max-width: 1280px;
  margin: 0 auto;
  padding: 32px 24px 64px;
}

.page-with-toc {
  display: grid;
  grid-template-columns: 240px 1fr;
  gap: 32px;
  align-items: start;
}

/* ── TOC ─────────────────────────────────────────────── */
.toc-sidebar {
  position: sticky;
  top: 80px;
  max-height: calc(100vh - 100px);
  overflow-y: auto;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 16px;
}

.toc-title {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--muted);
  margin-bottom: 10px;
}

.toc-list { list-style: none; }

.toc-list a {
  display: block;
  padding: 6px 10px;
  border-radius: 6px;
  text-decoration: none;
  color: var(--text2);
  font-size: 13px;
  transition: background 0.1s, color 0.1s;
  border: 1px solid transparent;
}

.toc-list a:hover {
  background: var(--card2);
  color: var(--text);
}

.toc-list a.toc-sub {
  padding-left: 20px;
  font-size: 12px;
  color: var(--muted);
}

/* ── Cards & Containers ─────────────────────────────── */
.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px;
  box-shadow: var(--shadow);
}

.card-sm {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
}

.card-hover {
  transition: border-color 0.2s, transform 0.2s, box-shadow 0.2s;
  cursor: pointer;
}

.card-hover:hover {
  border-color: var(--orange);
  transform: translateY(-2px);
  box-shadow: 0 8px 32px rgba(249,115,22,0.12);
}

/* ── Typography ─────────────────────────────────────── */
h1 { font-size: 2.2rem; font-weight: 800; line-height: 1.2; letter-spacing: -0.02em; }
h2 { font-size: 1.5rem; font-weight: 700; line-height: 1.3; }
h3 { font-size: 1.15rem; font-weight: 600; }
h4 { font-size: 1rem; font-weight: 600; }

.section-title {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 44px 0 20px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
  color: var(--text);
}

.section-title:first-child { margin-top: 0; }

.week-badge {
  background: var(--orange-glow);
  color: var(--orange);
  border: 1px solid rgba(249,115,22,0.3);
  font-size: 11px;
  font-weight: 700;
  padding: 2px 8px;
  border-radius: 20px;
  white-space: nowrap;
}

.subsection-title {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text);
  margin: 28px 0 12px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.subsection-title::before {
  content: '';
  display: inline-block;
  width: 4px;
  height: 18px;
  background: var(--orange);
  border-radius: 2px;
  flex-shrink: 0;
}

p { margin-bottom: 14px; color: var(--text2); }
strong { color: var(--text); font-weight: 600; }

/* ── Code ───────────────────────────────────────────── */
pre {
  margin: 16px 0;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  overflow-x: auto;
  font-size: 13px;
  line-height: 1.6;
}

code {
  font-family: var(--font-mono);
}

:not(pre) > code {
  background: var(--card2);
  border: 1px solid var(--border);
  padding: 1px 6px;
  border-radius: 4px;
  font-size: 12.5px;
  color: var(--orange);
}

.code-block-wrapper {
  position: relative;
  margin: 16px 0;
}

.code-label {
  display: inline-block;
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
  background: var(--card2);
  border: 1px solid var(--border);
  border-bottom: none;
  padding: 4px 12px;
  border-radius: 6px 6px 0 0;
}

.code-block-wrapper pre {
  margin-top: 0;
  border-radius: 0 var(--radius) var(--radius);
}

/* ── Callouts ───────────────────────────────────────── */
.callout {
  border-radius: var(--radius);
  padding: 16px 20px;
  margin: 20px 0;
  border-left: 4px solid;
}

.callout-title {
  font-weight: 700;
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 8px;
}

.callout-body { font-size: 14px; color: var(--text2); }
.callout-body ul { padding-left: 18px; margin-top: 6px; }
.callout-body li { margin-bottom: 4px; }

.callout-info    { background: var(--blue-glow);   border-color: var(--blue);   }
.callout-info .callout-title    { color: var(--blue);   }

.callout-warning { background: var(--yellow-glow); border-color: var(--yellow); }
.callout-warning .callout-title { color: var(--yellow); }

.callout-danger  { background: var(--red-glow);    border-color: var(--red);    }
.callout-danger .callout-title  { color: var(--red);   }

.callout-success { background: var(--green-glow);  border-color: var(--green);  }
.callout-success .callout-title { color: var(--green);  }

.callout-key     { background: var(--orange-glow); border-color: var(--orange); }
.callout-key .callout-title     { color: var(--orange); }

.callout-tip     { background: var(--purple-glow); border-color: var(--purple); }
.callout-tip .callout-title     { color: var(--purple); }

/* ── Tables ─────────────────────────────────────────── */
.table-wrap { overflow-x: auto; margin: 16px 0; }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
}

th {
  background: var(--card2);
  color: var(--text);
  font-weight: 600;
  text-align: left;
  padding: 10px 14px;
  border: 1px solid var(--border);
  font-size: 13px;
}

td {
  padding: 9px 14px;
  border: 1px solid var(--border);
  color: var(--text2);
  vertical-align: top;
}

tr:nth-child(even) td { background: rgba(255,255,255,0.02); }
tr:hover td { background: var(--orange-glow); }

/* ── Lists ──────────────────────────────────────────── */
.content-list {
  padding-left: 0;
  list-style: none;
  margin: 12px 0;
}

.content-list li {
  padding: 6px 0 6px 26px;
  position: relative;
  color: var(--text2);
  font-size: 14px;
  border-bottom: 1px solid rgba(255,255,255,0.04);
}

.content-list li::before {
  content: '▸';
  position: absolute;
  left: 8px;
  color: var(--orange);
  font-size: 12px;
}

/* ── Home Page ──────────────────────────────────────── */
.hero {
  text-align: center;
  padding: 48px 0 32px;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: var(--orange-glow);
  border: 1px solid rgba(249,115,22,0.3);
  color: var(--orange);
  font-size: 12px;
  font-weight: 700;
  padding: 6px 16px;
  border-radius: 20px;
  margin-bottom: 20px;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.hero h1 {
  font-size: 3rem;
  margin-bottom: 12px;
  background: linear-gradient(135deg, #f97316 0%, #fb923c 50%, #fdba74 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-sub {
  font-size: 1.1rem;
  color: var(--text2);
  max-width: 600px;
  margin: 0 auto 32px;
}

.hero-stats {
  display: flex;
  justify-content: center;
  gap: 32px;
  flex-wrap: wrap;
}

.stat-item {
  text-align: center;
}

.stat-num {
  font-size: 2rem;
  font-weight: 800;
  color: var(--orange);
  line-height: 1;
}

.stat-label {
  font-size: 12px;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-top: 4px;
}

/* ── Topic Cards ─────────────────────────────────────── */
.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 20px;
  margin: 32px 0;
}

.topic-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px;
  text-decoration: none;
  color: inherit;
  display: block;
  transition: border-color 0.2s, transform 0.2s, box-shadow 0.2s;
}

.topic-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.topic-card.threads-card:hover { border-color: var(--orange); box-shadow: 0 8px 40px rgba(249,115,22,0.15); }
.topic-card.network-card:hover { border-color: var(--blue);   box-shadow: 0 8px 40px rgba(59,130,246,0.15); }
.topic-card.security-card:hover{ border-color: var(--green);  box-shadow: 0 8px 40px rgba(16,185,129,0.15); }

.topic-icon {
  width: 52px;
  height: 52px;
  border-radius: 14px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 24px;
  margin-bottom: 16px;
}

.threads-icon  { background: var(--orange-glow); }
.network-icon  { background: var(--blue-glow);   }
.security-icon { background: var(--green-glow);  }

.topic-card h3 {
  font-size: 1.2rem;
  font-weight: 700;
  margin-bottom: 8px;
  color: var(--text);
}

.topic-card p {
  font-size: 14px;
  color: var(--muted);
  margin-bottom: 16px;
  line-height: 1.5;
}

.topic-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.tag {
  font-size: 11px;
  font-weight: 600;
  padding: 3px 9px;
  border-radius: 20px;
  border: 1px solid;
}

.tag-orange { background: var(--orange-glow); color: var(--orange); border-color: rgba(249,115,22,0.3); }
.tag-blue   { background: var(--blue-glow);   color: var(--blue);   border-color: rgba(59,130,246,0.3); }
.tag-green  { background: var(--green-glow);  color: var(--green);  border-color: rgba(16,185,129,0.3); }
.tag-purple { background: var(--purple-glow); color: var(--purple); border-color: rgba(139,92,246,0.3); }
.tag-yellow { background: var(--yellow-glow); color: var(--yellow); border-color: rgba(245,158,11,0.3); }
.tag-red    { background: var(--red-glow);    color: var(--red);    border-color: rgba(239,68,68,0.3); }

/* ── Buttons ─────────────────────────────────────────── */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  border-radius: var(--radius-sm);
  font-size: 14px;
  font-weight: 600;
  text-decoration: none;
  cursor: pointer;
  border: none;
  transition: background 0.15s, transform 0.1s, box-shadow 0.15s;
}

.btn:active { transform: scale(0.97); }

.btn-primary {
  background: var(--orange);
  color: #fff;
}
.btn-primary:hover { background: var(--orange-dim); }

.btn-outline {
  background: transparent;
  color: var(--text2);
  border: 1px solid var(--border2);
}
.btn-outline:hover { background: var(--card2); color: var(--text); }

.btn-blue   { background: var(--blue);  color: #fff; }
.btn-blue:hover { background: var(--blue-dim); }

.btn-green  { background: var(--green); color: #fff; }
.btn-green:hover { filter: brightness(0.9); }

.btn-lg { padding: 14px 28px; font-size: 15px; }
.btn-sm { padding: 6px 14px; font-size: 13px; }

/* ── Quiz ───────────────────────────────────────────── */
.quiz-container {
  max-width: 860px;
  margin: 0 auto;
}

.quiz-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 24px;
  flex-wrap: wrap;
  gap: 12px;
}

.quiz-progress-bar {
  height: 6px;
  background: var(--border);
  border-radius: 3px;
  margin-bottom: 28px;
  overflow: hidden;
}

.quiz-progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--orange), var(--yellow));
  border-radius: 3px;
  transition: width 0.4s ease;
}

.question-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 32px;
  margin-bottom: 20px;
}

.question-meta {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 16px;
  flex-wrap: wrap;
}

.question-num {
  font-size: 12px;
  font-weight: 700;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.question-topic-tag {
  font-size: 11px;
  font-weight: 700;
  padding: 2px 8px;
  border-radius: 20px;
}

.question-text {
  font-size: 17px;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 20px;
  line-height: 1.5;
}

.question-code {
  margin: 16px 0;
}

.options-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.option-btn {
  display: flex;
  align-items: flex-start;
  gap: 14px;
  padding: 14px 18px;
  background: var(--card2);
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  cursor: pointer;
  text-align: left;
  color: var(--text2);
  font-size: 14px;
  font-family: var(--font);
  transition: border-color 0.15s, background 0.15s, color 0.15s;
  width: 100%;
  line-height: 1.5;
}

.option-btn:hover:not(:disabled) {
  border-color: var(--orange);
  background: var(--orange-glow);
  color: var(--text);
}

.option-btn.correct {
  border-color: var(--green);
  background: var(--green-glow);
  color: var(--text);
}

.option-btn.wrong {
  border-color: var(--red);
  background: var(--red-glow);
  color: var(--text);
}

.option-letter {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border-radius: 6px;
  background: var(--border);
  color: var(--muted);
  font-size: 12px;
  font-weight: 700;
  flex-shrink: 0;
  margin-top: 1px;
}

.option-btn.correct .option-letter { background: var(--green); color: #fff; }
.option-btn.wrong .option-letter   { background: var(--red);   color: #fff; }

.explanation-box {
  display: none;
  margin-top: 16px;
  padding: 16px 20px;
  background: var(--bg2);
  border: 1px solid var(--border2);
  border-radius: var(--radius);
  font-size: 14px;
  color: var(--text2);
  line-height: 1.6;
}

.explanation-box.show { display: block; animation: fadeIn 0.3s ease; }

.explanation-box strong { color: var(--orange); }

.quiz-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 24px;
  flex-wrap: wrap;
  gap: 12px;
}

/* ── Quiz Setup Screen ───────────────────────────────── */
.quiz-setup {
  max-width: 640px;
  margin: 0 auto;
}

.filter-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 12px;
  margin: 16px 0;
}

.filter-btn {
  padding: 12px 16px;
  border: 2px solid var(--border);
  border-radius: var(--radius);
  background: var(--card2);
  color: var(--text2);
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  text-align: center;
  transition: border-color 0.15s, background 0.15s, color 0.15s;
  font-family: var(--font);
}

.filter-btn:hover { border-color: var(--orange); color: var(--text); }
.filter-btn.selected { border-color: var(--orange); background: var(--orange-glow); color: var(--orange); }

/* ── Results Screen ──────────────────────────────────── */
.results-screen { text-align: center; }

.score-circle {
  width: 140px;
  height: 140px;
  border-radius: 50%;
  border: 6px solid var(--orange);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  margin: 0 auto 24px;
  background: var(--orange-glow);
}

.score-num {
  font-size: 2.8rem;
  font-weight: 800;
  color: var(--orange);
  line-height: 1;
}

.score-label {
  font-size: 12px;
  color: var(--muted);
  margin-top: 4px;
}

.results-breakdown {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 12px;
  margin: 24px 0;
  text-align: left;
}

.breakdown-item {
  background: var(--card2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px 18px;
}

.breakdown-label {
  font-size: 12px;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 6px;
}

.breakdown-val {
  font-size: 1.4rem;
  font-weight: 800;
  color: var(--text);
}

/* ── Cheatsheet ──────────────────────────────────────── */
.cheat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 20px;
  margin: 20px 0;
}

.cheat-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}

.cheat-head {
  padding: 12px 16px;
  font-size: 13px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  border-bottom: 1px solid var(--border);
}

.cheat-head-orange { background: var(--orange-glow); color: var(--orange); }
.cheat-head-blue   { background: var(--blue-glow);   color: var(--blue);   }
.cheat-head-green  { background: var(--green-glow);  color: var(--green);  }
.cheat-head-purple { background: var(--purple-glow); color: var(--purple); }

.cheat-body {
  padding: 16px;
}

.cheat-body pre {
  margin: 0;
  font-size: 12px;
  border: none;
  background: transparent;
}

/* ── Comparison Grid ─────────────────────────────────── */
.compare-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin: 20px 0;
}

.compare-item {
  background: var(--card2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
}

.compare-item h4 {
  font-size: 14px;
  font-weight: 700;
  margin-bottom: 10px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}

/* ── Steps / How-it-works ────────────────────────────── */
.steps-list {
  list-style: none;
  counter-reset: step-counter;
  margin: 16px 0;
}

.steps-list li {
  counter-increment: step-counter;
  display: flex;
  gap: 14px;
  padding: 14px 0;
  border-bottom: 1px solid var(--border);
  color: var(--text2);
  font-size: 14px;
  line-height: 1.5;
}

.steps-list li::before {
  content: counter(step-counter);
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--orange);
  color: #fff;
  font-size: 12px;
  font-weight: 800;
  flex-shrink: 0;
}

/* ── Definition Term ─────────────────────────────────── */
.def-grid {
  display: grid;
  gap: 10px;
  margin: 16px 0;
}

.def-item {
  background: var(--card2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 14px 16px;
  display: grid;
  grid-template-columns: 180px 1fr;
  gap: 12px;
  align-items: start;
}

.def-term {
  font-weight: 700;
  color: var(--orange);
  font-size: 14px;
}

.def-desc {
  font-size: 14px;
  color: var(--text2);
  line-height: 1.5;
}

/* ── Toast ───────────────────────────────────────────── */
.toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(100px);
  background: var(--card);
  border: 1px solid var(--border2);
  color: var(--text);
  padding: 12px 24px;
  border-radius: var(--radius);
  font-size: 14px;
  font-weight: 600;
  box-shadow: var(--shadow-lg);
  transition: transform 0.3s ease;
  z-index: 999;
  white-space: nowrap;
}

.toast.show { transform: translateX(-50%) translateY(0); }

/* ── Section Divider ─────────────────────────────────── */
.divider {
  border: none;
  border-top: 1px solid var(--border);
  margin: 32px 0;
}

/* ── Animations ──────────────────────────────────────── */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to   { opacity: 1; transform: translateY(0); }
}

.fade-in { animation: fadeIn 0.4s ease; }

/* ── Subnet Calculator ────────────────────────────────── */
.subnet-calc-card {
  background: var(--card);
  border: 1px solid var(--border2);
  border-radius: var(--radius);
  overflow: hidden;
  margin: 24px 0;
}

.subnet-tabs {
  display: flex;
  border-bottom: 1px solid var(--border);
  background: var(--bg2);
}

.stab {
  padding: 12px 20px;
  background: none;
  border: none;
  color: var(--muted);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  border-bottom: 2px solid transparent;
  transition: color 0.15s, border-color 0.15s;
}
.stab:hover { color: var(--text); }
.stab.active { color: var(--orange); border-bottom-color: var(--orange); }

.stab-content { padding: 24px; }

.calc-label {
  display: block;
  font-size: 12px;
  font-weight: 700;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 6px;
}

.calc-input {
  background: var(--bg2);
  border: 1px solid var(--border2);
  border-radius: var(--radius-sm);
  color: var(--text);
  padding: 8px 12px;
  font-size: 14px;
  font-family: 'JetBrains Mono', monospace;
  width: 160px;
  outline: none;
  transition: border-color 0.15s;
}
.calc-input:focus { border-color: var(--orange); }

/* Binary display */
.subnet-result { animation: fadeIn 0.3s ease; }

.bin-table {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 16px 20px;
  margin-bottom: 12px;
  overflow-x: auto;
}

.bin-row {
  display: flex;
  align-items: center;
  gap: 4px;
  margin-bottom: 8px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 13px;
  flex-wrap: nowrap;
}
.bin-row:last-child { margin-bottom: 0; }

.bin-row.bin-and {
  border-top: 1px solid var(--border2);
  padding-top: 8px;
  margin-top: 4px;
}

.bin-label {
  color: var(--muted);
  font-size: 12px;
  min-width: 56px;
  flex-shrink: 0;
}

.bn {
  display: inline-block;
  width: 14px;
  text-align: center;
  font-weight: 700;
  font-size: 13px;
}
.bn-net  { color: var(--orange); }
.bn-host { color: var(--blue); }
.bn-sep  { color: var(--muted); padding: 0 3px; }

.legend {
  font-size: 12px;
  color: var(--muted);
  display: flex;
  gap: 20px;
}

/* Result grid */
.sn-result-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 10px;
  margin-top: 8px;
}

.sn-res-item {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 12px 16px;
}

.sn-res-item.sn-hi {
  border-color: rgba(249,115,22,0.4);
  background: var(--orange-glow);
}

.sn-label {
  display: block;
  font-size: 11px;
  font-weight: 700;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 4px;
}

.sn-val {
  font-size: 16px;
  font-weight: 700;
  color: var(--text);
  font-family: 'JetBrains Mono', monospace;
}

/* Practice mode */
.practice-q {
  background: var(--bg2);
  border: 1px solid var(--border2);
  border-radius: var(--radius);
  padding: 20px;
}

.practice-qtext {
  font-size: 15px;
  color: var(--text2);
  margin-bottom: 20px;
  line-height: 1.6;
}

.practice-inputs { display: flex; flex-direction: column; gap: 12px; }

.pi-row {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
}

.pi-row label {
  font-size: 13px;
  color: var(--text2);
  min-width: 260px;
  flex-shrink: 0;
}

.pi-row input {
  background: var(--card);
  border: 1px solid var(--border2);
  border-radius: var(--radius-sm);
  color: var(--text);
  padding: 7px 12px;
  font-size: 14px;
  font-family: 'JetBrains Mono', monospace;
  width: 180px;
  outline: none;
}
.pi-row input:focus { border-color: var(--orange); }

/* Practice verdict */
.practice-verdict {
  margin-top: 20px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.pv-row {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 10px 14px;
  border-radius: var(--radius-sm);
  font-size: 13px;
  line-height: 1.5;
}

.pv-ok  { background: rgba(16,185,129,0.12); border: 1px solid rgba(16,185,129,0.3); color: var(--text2); }
.pv-fail{ background: rgba(239,68,68,0.12);  border: 1px solid rgba(239,68,68,0.3);  color: var(--text2); }

.pv-icon { font-size: 16px; flex-shrink: 0; margin-top: 1px; }
.pv-ok  .pv-icon { color: var(--green); }
.pv-fail .pv-icon { color: var(--red); }

.pv-score {
  margin-top: 8px;
  text-align: center;
  font-size: 16px;
  font-weight: 700;
  color: var(--text);
  padding: 12px;
  background: var(--card2);
  border-radius: var(--radius-sm);
}

/* ── Slides Page ─────────────────────────────────────── */
.slides-grid { display:grid; grid-template-columns:repeat(auto-fill,minmax(260px,1fr)); gap:16px; }
.slide-card { display:flex; flex-direction:column; gap:10px; background:var(--card); border:1px solid var(--border); border-radius:16px; padding:18px 20px; text-decoration:none; color:var(--text); transition:transform 0.18s,box-shadow 0.18s,border-color 0.18s; }
.slide-card:hover { transform:translateY(-3px); box-shadow:0 12px 32px var(--card-glow,rgba(0,0,0,0.2)); border-color:var(--card-color,var(--border)); }
.sc-head { display:flex; align-items:center; justify-content:space-between; }
.sc-badge { font-size:11px; font-weight:800; padding:3px 10px; border-radius:999px; letter-spacing:0.02em; }
.sc-slides { font-size:11px; color:var(--muted); }
.sc-title { font-size:14px; font-weight:700; line-height:1.4; color:var(--text); }
.sc-desc { font-size:12px; color:var(--text2); line-height:1.5; flex:1; }
.sc-open { display:flex; align-items:center; gap:5px; font-size:12px; font-weight:600; color:var(--card-color,var(--orange)); margin-top:4px; }
.slide-card:hover .sc-open { text-decoration:underline; }

/* ── Sim Tab Bar ─────────────────────────────────────── */
.sim-tab-bar { display:flex; gap:0; margin-bottom:20px; border-bottom:1px solid var(--border); }
.sim-tab { background:none; border:none; border-bottom:2px solid transparent; padding:8px 18px; color:var(--text2); font-size:13.5px; font-weight:600; cursor:pointer; margin-bottom:-1px; transition:color 0.15s,border-color 0.15s; }
.sim-tab:hover { color:var(--text); }
.sim-tab.active { color:var(--orange); border-bottom-color:var(--orange); }
.tsq-opt { width:100%; text-align:left; transition:background 0.15s,border-color 0.15s; }
.tsq-opt:disabled { cursor:default; }
.tsq-letter { font-weight:700; color:var(--orange); margin-right:8px; }

/* ── Thread State Simulator ──────────────────────────── */
.thread-sim-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 24px; }
.ts-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
  margin-bottom: 20px;
}
.ts-box {
  border: 2px solid var(--border);
  border-radius: 8px;
  padding: 10px 8px;
  text-align: center;
  opacity: 0.3;
  transition: opacity 0.25s, box-shadow 0.25s, border-color 0.25s;
  cursor: default;
}
.ts-box.ts-active { opacity: 1; }
.ts-box .ts-name { font-weight: 700; font-size: 12px; letter-spacing: 0.04em; }
.ts-box .ts-sub  { font-size: 10px; opacity: 0.75; margin-top: 3px; }
.ts-new          { border-color: #6b7280; color: #6b7280; }
.ts-new.ts-active { box-shadow: 0 0 14px #6b728060; }
.ts-runnable     { border-color: var(--green); color: var(--green); }
.ts-runnable.ts-active { box-shadow: 0 0 14px var(--green-glow); }
.ts-blocked      { border-color: var(--orange); color: var(--orange); }
.ts-blocked.ts-active  { box-shadow: 0 0 14px var(--orange-glow); }
.ts-waiting      { border-color: var(--blue); color: var(--blue); }
.ts-waiting.ts-active  { box-shadow: 0 0 14px var(--blue-glow); }
.ts-timed        { border-color: #a78bfa; color: #a78bfa; }
.ts-timed.ts-active    { box-shadow: 0 0 14px #a78bfa40; }
.ts-terminated   { border-color: var(--red); color: var(--red); }
.ts-terminated.ts-active { box-shadow: 0 0 14px #ef444440; }

.sim-status { background: var(--card2); border-radius: 8px; padding: 14px 16px; margin-bottom: 16px; }
.sim-state-label { font-size: 12px; font-weight: 700; color: var(--muted); text-transform: uppercase; letter-spacing: 0.06em; margin-bottom: 6px; }
.sim-cur-badge { font-size: 14px; font-weight: 800; padding: 2px 10px; border-radius: 20px; background: var(--card); border: 1px solid var(--border); }
.sim-explain { font-size: 13.5px; line-height: 1.6; margin: 8px 0 0; color: var(--text2); }
.sim-btn-row { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 16px; }
.sim-btn-row .btn { font-size: 12.5px; font-family: var(--mono); }
.sim-log { background: var(--card2); border-radius: 8px; padding: 12px 14px; max-height: 140px; overflow-y: auto; }
.sim-log-title { font-size: 11px; font-weight: 700; color: var(--muted); text-transform: uppercase; margin-bottom: 8px; }
.sim-log-entry { font-size: 12px; padding: 4px 0; border-bottom: 1px solid var(--border); display: flex; align-items: center; gap: 6px; }
.sim-log-entry:last-child { border-bottom: none; }
.sim-log-entry code { font-size: 11px; background: var(--card); padding: 1px 5px; border-radius: 4px; }
.sim-badge { font-size: 11px; font-weight: 700; padding: 1px 7px; border-radius: 10px; background: var(--card); border: 1px solid currentColor; }

/* ── Crypto Lab ───────────────────────────────────────── */
.crypto-lab { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 24px; }
.crypto-tabs { display: flex; gap: 4px; margin-bottom: 20px; border-bottom: 1px solid var(--border); }
.ctab { background: none; border: none; border-bottom: 2px solid transparent; padding: 8px 16px; color: var(--text2); font-size: 13.5px; font-weight: 600; cursor: pointer; margin-bottom: -1px; transition: color 0.15s, border-color 0.15s; }
.ctab:hover { color: var(--text); }
.ctab.active { color: var(--green); border-bottom-color: var(--green); }
.ctab-content { display: none; }
.ctab-content.active { display: block; }
.crypto-textarea {
  width: 100%; box-sizing: border-box;
  background: var(--card2); border: 1px solid var(--border); border-radius: 8px;
  color: var(--text); font-family: var(--mono); font-size: 13px;
  padding: 10px 12px; resize: vertical; outline: none;
  transition: border-color 0.15s;
}
.crypto-textarea:focus { border-color: var(--green); }
.crypto-result { background: var(--card2); border: 1px solid var(--border); border-radius: 8px; padding: 14px 16px; margin-top: 12px; }
.cr-label { font-size: 11px; font-weight: 700; color: var(--muted); text-transform: uppercase; letter-spacing: 0.06em; margin-bottom: 8px; }
.cr-output { display: block; font-family: var(--mono); font-size: 12px; word-break: break-all; color: var(--green); padding: 4px 0; }
.cr-meta { font-size: 11px; color: var(--muted); margin-top: 6px; }
.crypto-key-box { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; margin-bottom: 14px; }
.crypto-key-val { font-family: var(--mono); font-size: 11px; color: var(--blue); word-break: break-all; background: var(--card2); border: 1px solid var(--border); border-radius: 6px; padding: 6px 10px; flex: 1; min-width: 0; }
.crypto-row { display: flex; gap: 8px; margin: 10px 0; }
.crypto-section-label { font-size: 12px; font-weight: 700; color: var(--muted); text-transform: uppercase; margin: 14px 0 6px; }

/* ── Analysis Page ───────────────────────────────────── */
.analysis-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 16px; margin-bottom: 32px; }
.an-stat { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 20px; text-align: center; }
.an-stat-num { font-size: 2.2rem; font-weight: 800; }
.an-stat-label { font-size: 12px; color: var(--muted); text-transform: uppercase; letter-spacing: 0.06em; margin-top: 4px; }
.an-section { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 24px; margin-bottom: 24px; }
.an-section-title { font-size: 15px; font-weight: 700; margin-bottom: 18px; display: flex; align-items: center; gap: 8px; }
.mastery-row { display: flex; align-items: center; gap: 12px; margin-bottom: 14px; }
.mastery-label { width: 110px; font-size: 13px; font-weight: 600; flex-shrink: 0; }
.mastery-bar-wrap { flex: 1; background: var(--card2); border-radius: 99px; height: 10px; overflow: hidden; }
.mastery-bar { height: 100%; border-radius: 99px; transition: width 0.8s ease; }
.mastery-pct { width: 42px; text-align: right; font-size: 13px; font-weight: 700; flex-shrink: 0; }
.trend-bars { display: flex; align-items: flex-end; gap: 6px; height: 80px; }
.trend-bar-wrap { flex: 1; display: flex; flex-direction: column; align-items: center; gap: 4px; height: 100%; justify-content: flex-end; }
.trend-bar { width: 100%; border-radius: 4px 4px 0 0; min-height: 4px; transition: height 0.5s; }
.trend-bar-label { font-size: 10px; color: var(--muted); white-space: nowrap; }
.weak-q-row { padding: 12px 0; border-bottom: 1px solid var(--border); display: flex; align-items: flex-start; gap: 12px; }
.weak-q-row:last-child { border-bottom: none; }
.weak-q-acc { width: 44px; font-size: 13px; font-weight: 700; text-align: center; flex-shrink: 0; padding: 4px 0; border-radius: 6px; background: var(--card2); }
.weak-q-text { flex: 1; font-size: 13px; color: var(--text2); line-height: 1.5; }
.weak-q-tags { display: flex; gap: 6px; margin-top: 4px; flex-wrap: wrap; }
.an-empty { text-align: center; padding: 48px 24px; color: var(--muted); }
.an-empty svg { opacity: 0.2; margin-bottom: 16px; }
.rec-row { display: flex; align-items: center; justify-content: space-between; gap: 16px; padding: 12px 0; border-bottom: 1px solid var(--border); flex-wrap: wrap; }
.rec-row:last-child { border-bottom: none; }
.rec-text { font-size: 13.5px; }

/* ── Footer ──────────────────────────────────────────── */
.site-footer {
  border-top: 1px solid var(--border);
  padding: 28px 24px;
  text-align: center;
}

.footer-inner p {
  color: var(--muted);
  font-size: 13px;
  margin-bottom: 4px;
}

.footer-sub { font-size: 12px !important; letter-spacing: 0.05em; }

/* ── Responsive ──────────────────────────────────────── */
@media (max-width: 900px) {
  .page-with-toc {
    grid-template-columns: 1fr;
  }

  .toc-sidebar {
    position: relative;
    top: auto;
    max-height: none;
    display: none;
  }

  .nav-toggle { display: block; }

  .lang-switch { margin-left: auto; border-left: none; padding-left: 0; }

  .nav-links {
    display: none;
    flex-direction: column;
    position: absolute;
    top: 60px;
    left: 0;
    right: 0;
    background: var(--bg);
    border-bottom: 1px solid var(--border);
    padding: 12px 16px;
    gap: 4px;
  }

  .nav-links.open { display: flex; }

  .topnav { position: relative; }

  .hero h1 { font-size: 2rem; }

  .compare-grid { grid-template-columns: 1fr; }

  .def-item { grid-template-columns: 1fr; }
}

@media (max-width: 600px) {
  .main-content { padding: 20px 16px 48px; }
  .card { padding: 20px; }
  .question-card { padding: 20px; }
  h1 { font-size: 1.6rem; }
}