@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800&family=JetBrains+Mono:wght@400;500&display=swap');

/* ===== CSS VARIABLES ===== */
:root {
  --color-bg: #0f172a;
  --color-surface: #1e293b;
  --color-surface-2: #263348;
  --color-border: #334155;
  --color-text: #f1f5f9;
  --color-text-muted: #94a3b8;
  --color-text-dim: #64748b;
  --color-primary: #6366f1;
  --color-primary-hover: #818cf8;
  --color-primary-dim: rgba(99,102,241,0.15);
  --color-success: #10b981;
  --color-success-dim: rgba(16,185,129,0.15);
  --color-warning: #f59e0b;
  --color-warning-dim: rgba(245,158,11,0.15);
  --color-danger: #ef4444;
  --color-danger-dim: rgba(239,68,68,0.15);
  --color-info: #3b82f6;
  --color-info-dim: rgba(59,130,246,0.15);
  --color-locked: #475569;
  --sidebar-width: 280px;
  --header-height: 60px;
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  --shadow-md: 0 4px 12px rgba(0,0,0,0.4);
  --shadow-lg: 0 8px 24px rgba(0,0,0,0.5);
  --transition: 200ms ease;
}

/* ===== RESET ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; font-size: 16px; }
body { font-family: var(--font-sans); background: var(--color-bg); color: var(--color-text); line-height: 1.6; -webkit-font-smoothing: antialiased; }
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: var(--color-bg); }
::-webkit-scrollbar-thumb { background: var(--color-border); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--color-text-dim); }

/* ===== LAYOUT ===== */
.app-layout { display: flex; min-height: 100vh; }

/* ===== SIDEBAR ===== */
.sidebar {
  width: var(--sidebar-width);
  background: var(--color-surface);
  border-right: 1px solid var(--color-border);
  position: fixed; top: 0; left: 0;
  height: 100vh; overflow-y: auto;
  z-index: 100;
  display: flex; flex-direction: column;
  transition: transform var(--transition);
}
.sidebar-logo {
  padding: 1.25rem 1.5rem;
  border-bottom: 1px solid var(--color-border);
  flex-shrink: 0;
}
.sidebar-logo a { text-decoration: none; display: flex; align-items: center; gap: 0.625rem; }
.logo-icon {
  width: 34px; height: 34px;
  background: linear-gradient(135deg, var(--color-primary), #8b5cf6);
  border-radius: var(--radius-md);
  display: flex; align-items: center; justify-content: center;
  font-size: 18px; flex-shrink: 0;
}
.logo-text { font-size: 0.8125rem; font-weight: 700; color: var(--color-text); line-height: 1.2; }
.logo-subtitle { font-size: 0.6875rem; color: var(--color-text-muted); font-weight: 400; }
.sidebar-progress { padding: 0.75rem 1.5rem; border-bottom: 1px solid var(--color-border); flex-shrink: 0; }
.sidebar-progress-label { display: flex; justify-content: space-between; font-size: 0.6875rem; color: var(--color-text-muted); margin-bottom: 6px; }
.progress-bar { height: 4px; background: var(--color-border); border-radius: 2px; overflow: hidden; }
.progress-bar-fill { height: 100%; background: linear-gradient(90deg, var(--color-primary), var(--color-success)); border-radius: 2px; transition: width 600ms ease; }
.module-list { list-style: none; padding: 0.5rem 0; flex: 1; overflow-y: auto; }
.module-list-link {
  display: flex; align-items: flex-start; gap: 0.5rem;
  padding: 0.5rem 1.5rem;
  text-decoration: none; font-size: 0.75rem; color: var(--color-text-muted);
  border-left: 3px solid transparent;
  transition: all var(--transition); cursor: pointer;
}
.module-list-link:hover:not(.locked) { background: var(--color-surface-2); color: var(--color-text); border-left-color: var(--color-primary); }
.module-list-link.active { background: var(--color-primary-dim); color: var(--color-primary-hover); border-left-color: var(--color-primary); font-weight: 600; }
.module-list-link.completed { color: var(--color-success); }
.module-list-link.locked { opacity: 0.4; cursor: not-allowed; }
.module-num { font-size: 0.6875rem; font-weight: 700; min-width: 22px; color: var(--color-text-dim); font-family: var(--font-mono); flex-shrink: 0; margin-top: 1px; }
.module-title-text { flex: 1; line-height: 1.35; }
.module-status-icon { font-size: 0.6875rem; flex-shrink: 0; margin-top: 2px; }

/* ===== MAIN WRAPPER ===== */
.main-wrapper { margin-left: var(--sidebar-width); flex: 1; display: flex; flex-direction: column; min-height: 100vh; }
.top-header {
  height: var(--header-height);
  background: var(--color-surface); border-bottom: 1px solid var(--color-border);
  display: flex; align-items: center; padding: 0 2rem;
  position: sticky; top: 0; z-index: 50; gap: 1rem;
}
.hamburger { display: none; background: none; border: none; cursor: pointer; color: var(--color-text); font-size: 1.25rem; padding: 0.25rem; }
.breadcrumb { display: flex; align-items: center; gap: 0.5rem; font-size: 0.8125rem; color: var(--color-text-muted); flex: 1; min-width: 0; }
.breadcrumb a { color: var(--color-text-muted); text-decoration: none; transition: color var(--transition); white-space: nowrap; }
.breadcrumb a:hover { color: var(--color-primary-hover); }
.breadcrumb-sep { color: var(--color-text-dim); }
.breadcrumb-current { color: var(--color-text); font-weight: 500; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.sidebar-overlay { display: none; position: fixed; inset: 0; background: rgba(0,0,0,0.6); z-index: 99; }
.sidebar-overlay.visible { display: block; }

/* ===== CONTENT ===== */
.content { max-width: 900px; margin: 0 auto; padding: 2.5rem 2rem; flex: 1; width: 100%; }
.module-header { margin-bottom: 2.5rem; padding-bottom: 2rem; border-bottom: 1px solid var(--color-border); }
.module-tag {
  display: inline-flex; align-items: center; gap: 0.25rem;
  background: var(--color-primary-dim); color: var(--color-primary-hover);
  font-size: 0.6875rem; font-weight: 700; padding: 3px 10px;
  border-radius: var(--radius-sm); text-transform: uppercase; letter-spacing: 0.07em; margin-bottom: 1rem;
}
.module-header h1 { font-size: 2rem; font-weight: 800; line-height: 1.15; margin-bottom: 1rem; }
.module-meta { display: flex; align-items: center; gap: 1.5rem; flex-wrap: wrap; }
.meta-item { display: flex; align-items: center; gap: 0.35rem; font-size: 0.8125rem; color: var(--color-text-muted); }

/* ===== TYPOGRAPHY ===== */
.content h2 {
  font-size: 1.375rem; font-weight: 700;
  margin: 2.5rem 0 1rem; color: var(--color-text);
  display: flex; align-items: center; gap: 0.625rem;
}
.content h2::before {
  content: ''; display: inline-block; width: 4px; height: 1.1em;
  background: var(--color-primary); border-radius: 2px; flex-shrink: 0;
}
.content h3 { font-size: 1.0625rem; font-weight: 600; margin: 1.75rem 0 0.75rem; color: var(--color-text); }
.content h4 { font-size: 0.75rem; font-weight: 700; margin: 1.25rem 0 0.5rem; color: var(--color-text-dim); text-transform: uppercase; letter-spacing: 0.08em; }
.content p { margin-bottom: 1rem; line-height: 1.75; }
.content ul, .content ol { margin: 0.75rem 0 1rem 1.5rem; }
.content li { margin-bottom: 0.4rem; line-height: 1.6; }
.content a { color: var(--color-primary-hover); text-decoration: none; border-bottom: 1px solid transparent; transition: border-color var(--transition); }
.content a:hover { border-bottom-color: var(--color-primary-hover); }
code:not(pre code) {
  font-family: var(--font-mono); font-size: 0.85em;
  background: var(--color-surface-2); border: 1px solid var(--color-border);
  border-radius: var(--radius-sm); padding: 0.1em 0.4em; color: #f472b6;
}
hr.divider { border: none; border-top: 1px solid var(--color-border); margin: 2.5rem 0; }

/* ===== CODE BLOCKS ===== */
.code-block { margin: 1.5rem 0; border-radius: var(--radius-lg); overflow: hidden; border: 1px solid #30363d; box-shadow: var(--shadow-md); }
.code-block-header { display: flex; align-items: center; justify-content: space-between; background: #161b22; padding: 0.5rem 1rem; border-bottom: 1px solid #30363d; }
.code-block-title { font-family: var(--font-mono); font-size: 0.75rem; color: #8b949e; display: flex; align-items: center; gap: 0.5rem; }
.code-lang-badge { background: var(--color-primary-dim); color: var(--color-primary-hover); font-size: 0.625rem; font-weight: 700; padding: 2px 6px; border-radius: var(--radius-sm); text-transform: uppercase; letter-spacing: 0.06em; }
.copy-btn { background: transparent; border: 1px solid #30363d; border-radius: var(--radius-sm); color: #8b949e; cursor: pointer; font-size: 0.6875rem; padding: 4px 10px; transition: all var(--transition); font-family: var(--font-sans); display: flex; align-items: center; gap: 4px; }
.copy-btn:hover { background: #21262d; color: var(--color-text); border-color: #8b949e; }
.copy-btn.copied { background: var(--color-success-dim); color: var(--color-success); border-color: var(--color-success); }
.code-block pre { margin: 0; padding: 1.25rem 1.5rem; overflow-x: auto; font-size: 0.8125rem; line-height: 1.65; background: #0d1117; }
.code-block pre code { font-family: var(--font-mono); background: transparent; border: none; padding: 0; color: inherit; font-size: inherit; }

/* ===== CALLOUT BOXES ===== */
.callout { border-radius: var(--radius-lg); padding: 1.125rem 1.25rem; margin: 1.25rem 0; border-left: 4px solid; display: flex; gap: 0.875rem; }
.callout-icon { font-size: 1.125rem; flex-shrink: 0; margin-top: 1px; }
.callout-content { flex: 1; }
.callout-title { font-weight: 700; font-size: 0.75rem; margin-bottom: 0.3rem; text-transform: uppercase; letter-spacing: 0.07em; }
.callout-body { font-size: 0.875rem; line-height: 1.65; color: var(--color-text-muted); }
.callout-body p { margin-bottom: 0.4rem; }
.callout-body p:last-child { margin-bottom: 0; }
.callout-body code { font-family: var(--font-mono); font-size: 0.85em; }
.callout.info { background: var(--color-info-dim); border-color: var(--color-info); }
.callout.info .callout-title { color: var(--color-info); }
.callout.tip { background: var(--color-success-dim); border-color: var(--color-success); }
.callout.tip .callout-title { color: var(--color-success); }
.callout.warning { background: var(--color-warning-dim); border-color: var(--color-warning); }
.callout.warning .callout-title { color: var(--color-warning); }
.callout.danger { background: var(--color-danger-dim); border-color: var(--color-danger); }
.callout.danger .callout-title { color: var(--color-danger); }

/* ===== CARDS ===== */
.card-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 1rem; margin: 1.25rem 0; }
.card { background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: 1.25rem; transition: border-color var(--transition); }
.card:hover { border-color: var(--color-primary); }
.card-icon { font-size: 1.5rem; margin-bottom: 0.625rem; }
.card-title { font-weight: 600; font-size: 0.875rem; margin-bottom: 0.3rem; color: var(--color-text); }
.card-desc { font-size: 0.8rem; color: var(--color-text-muted); line-height: 1.5; }

/* ===== TABLE ===== */
.table-wrap { overflow-x: auto; margin: 1.25rem 0; border-radius: var(--radius-lg); border: 1px solid var(--color-border); }
table { width: 100%; border-collapse: collapse; font-size: 0.875rem; }
thead th { background: var(--color-surface); color: var(--color-text); font-weight: 600; padding: 0.75rem 1rem; text-align: left; border-bottom: 1px solid var(--color-border); white-space: nowrap; }
tbody td { padding: 0.7rem 1rem; border-bottom: 1px solid var(--color-border); color: var(--color-text-muted); vertical-align: top; line-height: 1.5; }
tbody tr:last-child td { border-bottom: none; }
tbody tr:hover td { background: var(--color-surface); }
tbody tr:nth-child(even) td { background: rgba(30,41,59,0.4); }

/* ===== STEPS ===== */
.steps { list-style: none; padding: 0; margin: 1.25rem 0; counter-reset: step-counter; }
.steps > li { counter-increment: step-counter; display: flex; gap: 1rem; margin-bottom: 1.5rem; position: relative; }
.steps > li::before { content: counter(step-counter); display: flex; align-items: center; justify-content: center; width: 30px; height: 30px; background: var(--color-primary-dim); border: 2px solid var(--color-primary); border-radius: 50%; font-weight: 700; font-size: 0.8125rem; color: var(--color-primary-hover); flex-shrink: 0; margin-top: 2px; }
.steps > li:not(:last-child)::after { content: ''; position: absolute; left: 14px; top: 34px; bottom: -14px; width: 2px; background: var(--color-border); }
.step-content { flex: 1; }
.step-title { font-weight: 600; margin-bottom: 0.25rem; }
.step-desc { font-size: 0.875rem; color: var(--color-text-muted); line-height: 1.6; }

/* ===== ARCHITECTURE DIAGRAM ===== */
.arch-diagram { background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: 1.5rem; margin: 1.25rem 0; overflow-x: auto; }
.arch-diagram pre { font-family: var(--font-mono); font-size: 0.8125rem; color: var(--color-text-muted); line-height: 1.6; margin: 0; white-space: pre; }

/* ===== TABLE OF CONTENTS ===== */
.toc { background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: 1.25rem; margin-bottom: 2.5rem; }
.toc-title { font-size: 0.6875rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.1em; color: var(--color-text-dim); margin-bottom: 0.75rem; }
.toc-list { list-style: none; padding: 0; margin: 0; columns: 2; gap: 0; }
.toc-list li { break-inside: avoid; }
.toc-list a { font-size: 0.8rem; color: var(--color-text-muted); text-decoration: none; padding: 3px 0; display: flex; align-items: center; gap: 0.5rem; transition: color var(--transition); }
.toc-list a:hover { color: var(--color-primary-hover); }
.toc-list a::before { content: ''; width: 4px; height: 4px; border-radius: 50%; background: var(--color-text-dim); flex-shrink: 0; }
@media (max-width: 600px) { .toc-list { columns: 1; } }

/* ===== QUIZ ===== */
.quiz-container { background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-xl); padding: 2rem; margin: 2.5rem 0; }
.quiz-header { margin-bottom: 2rem; padding-bottom: 1.25rem; border-bottom: 1px solid var(--color-border); }
.quiz-badge { display: inline-flex; align-items: center; gap: 0.35rem; background: linear-gradient(135deg, #6366f1, #8b5cf6); color: white; font-size: 0.6875rem; font-weight: 700; padding: 3px 10px; border-radius: var(--radius-sm); text-transform: uppercase; letter-spacing: 0.07em; margin-bottom: 0.875rem; }
.quiz-header h2 { font-size: 1.375rem; margin-bottom: 0.5rem; }
.quiz-header h2::before { display: none; }
.quiz-meta { font-size: 0.875rem; color: var(--color-text-muted); }
.quiz-meta strong { color: var(--color-warning); }
.question-block { margin-bottom: 1.5rem; padding: 1.25rem; background: var(--color-bg); border-radius: var(--radius-lg); border: 1px solid var(--color-border); }
.question-number { font-size: 0.6875rem; font-weight: 700; color: var(--color-text-dim); text-transform: uppercase; letter-spacing: 0.07em; margin-bottom: 0.5rem; font-family: var(--font-mono); }
.question-text { font-size: 0.9375rem; font-weight: 500; line-height: 1.55; margin-bottom: 1rem; }
.options-list { list-style: none; padding: 0; display: flex; flex-direction: column; gap: 0.5rem; }
.option-item { display: flex; align-items: flex-start; gap: 0.625rem; padding: 0.625rem 0.875rem; border: 1px solid var(--color-border); border-radius: var(--radius-md); cursor: pointer; transition: all var(--transition); background: var(--color-surface); }
.option-item:hover:not(.disabled) { border-color: var(--color-primary); background: var(--color-primary-dim); }
.option-marker { width: 18px; height: 18px; border: 2px solid var(--color-border); border-radius: 50%; flex-shrink: 0; margin-top: 2px; display: flex; align-items: center; justify-content: center; transition: all var(--transition); }
.option-item.selected .option-marker { border-color: var(--color-primary); background: var(--color-primary); }
.option-item.selected .option-marker::after { content: ''; width: 6px; height: 6px; background: white; border-radius: 50%; }
.option-item.correct { border-color: var(--color-success) !important; background: var(--color-success-dim) !important; }
.option-item.wrong { border-color: var(--color-danger) !important; background: var(--color-danger-dim) !important; }
.option-item.disabled { cursor: default; pointer-events: none; }
.option-text { font-size: 0.875rem; line-height: 1.5; flex: 1; }
.question-explanation { margin-top: 0.875rem; padding: 0.875rem; background: var(--color-surface-2); border-radius: var(--radius-md); font-size: 0.8125rem; color: var(--color-text-muted); display: none; line-height: 1.65; border-left: 3px solid var(--color-primary); }
.question-explanation.visible { display: block; }
.question-explanation strong { color: var(--color-text); }
.quiz-actions { display: flex; justify-content: space-between; align-items: center; margin-top: 2rem; padding-top: 1.25rem; border-top: 1px solid var(--color-border); flex-wrap: wrap; gap: 1rem; }
.quiz-progress-text { font-size: 0.875rem; color: var(--color-text-muted); }
.quiz-result { margin-top: 2rem; padding: 2rem; border-radius: var(--radius-lg); text-align: center; display: none; }
.quiz-result.visible { display: block; }
.quiz-result.passed { background: var(--color-success-dim); border: 2px solid var(--color-success); }
.quiz-result.failed { background: var(--color-danger-dim); border: 2px solid var(--color-danger); }
.result-icon { font-size: 3rem; margin-bottom: 0.875rem; }
.result-score { font-size: 3rem; font-weight: 800; margin-bottom: 0.5rem; line-height: 1; }
.quiz-result.passed .result-score { color: var(--color-success); }
.quiz-result.failed .result-score { color: var(--color-danger); }
.result-message { font-size: 1.125rem; font-weight: 600; margin-bottom: 0.5rem; }
.result-detail { font-size: 0.875rem; color: var(--color-text-muted); margin-bottom: 1.25rem; line-height: 1.6; }

/* ===== BUTTONS ===== */
.btn { display: inline-flex; align-items: center; gap: 0.5rem; padding: 0.5rem 1.25rem; border-radius: var(--radius-md); font-weight: 600; font-size: 0.875rem; cursor: pointer; transition: all var(--transition); text-decoration: none; border: 2px solid transparent; font-family: var(--font-sans); }
.btn:hover { text-decoration: none; }
.btn-primary { background: var(--color-primary); color: white; border-color: var(--color-primary); }
.btn-primary:hover { background: var(--color-primary-hover); border-color: var(--color-primary-hover); color: white; }
.btn-secondary { background: transparent; color: var(--color-text); border-color: var(--color-border); }
.btn-secondary:hover { border-color: var(--color-primary); color: var(--color-primary-hover); }
.btn-success { background: var(--color-success); color: white; border-color: var(--color-success); }
.btn-lg { padding: 0.75rem 1.75rem; font-size: 1rem; }
.btn:disabled, .btn[disabled] { opacity: 0.4; cursor: not-allowed; pointer-events: none; }

/* ===== MODULE NAVIGATION ===== */
.module-nav-outer { background: var(--color-surface); border-top: 1px solid var(--color-border); }
.module-nav { display: flex; justify-content: space-between; align-items: center; padding: 1.5rem 2rem; max-width: 900px; margin: 0 auto; width: 100%; }
.nav-btn { display: flex; align-items: center; gap: 0.5rem; padding: 0.75rem 1.25rem; border-radius: var(--radius-md); text-decoration: none; font-weight: 600; font-size: 0.875rem; transition: all var(--transition); border: 2px solid var(--color-border); color: var(--color-text-muted); }
.nav-btn:hover:not(.disabled):not(.locked) { border-color: var(--color-primary); color: var(--color-primary-hover); }
.nav-btn.disabled { opacity: 0.3; cursor: not-allowed; pointer-events: none; }
.nav-btn-next { background: var(--color-primary); border-color: var(--color-primary); color: white; }
.nav-btn-next:hover:not(.locked) { background: var(--color-primary-hover); border-color: var(--color-primary-hover); color: white; }
.nav-btn-next.locked { background: var(--color-surface-2); border-color: var(--color-border); color: var(--color-text-dim); cursor: not-allowed; pointer-events: none; }

/* ===== INDEX PAGE ===== */
.index-header { background: var(--color-surface); border-bottom: 1px solid var(--color-border); padding: 1rem 2rem; display: flex; align-items: center; justify-content: space-between; position: sticky; top: 0; z-index: 100; }
.index-logo { display: flex; align-items: center; gap: 0.625rem; text-decoration: none; }
.index-logo-icon { width: 36px; height: 36px; background: linear-gradient(135deg, var(--color-primary), #8b5cf6); border-radius: var(--radius-md); display: flex; align-items: center; justify-content: center; font-size: 20px; }
.index-logo-name { font-weight: 700; font-size: 1rem; color: var(--color-text); }
.index-logo-name span { font-weight: 400; color: var(--color-text-muted); }
.index-header-actions { display: flex; align-items: center; gap: 1rem; }
.header-progress-wrap { display: flex; align-items: center; gap: 0.625rem; }
.header-progress-wrap span { font-size: 0.75rem; color: var(--color-text-muted); white-space: nowrap; }
.header-progress-bar { width: 120px; height: 4px; background: var(--color-border); border-radius: 2px; overflow: hidden; }
.header-progress-fill { height: 100%; background: linear-gradient(90deg, var(--color-primary), var(--color-success)); border-radius: 2px; transition: width 600ms ease; }

.hero { background: linear-gradient(135deg, #0f172a 0%, #1e1b4b 60%, #0f172a 100%); padding: 5rem 2rem; text-align: center; position: relative; overflow: hidden; }
.hero::before { content: ''; position: absolute; width: 700px; height: 700px; background: radial-gradient(circle, rgba(99,102,241,0.12) 0%, transparent 70%); top: 50%; left: 50%; transform: translate(-50%,-50%); pointer-events: none; }
.hero-eyebrow { display: inline-flex; align-items: center; gap: 0.5rem; background: var(--color-primary-dim); border: 1px solid rgba(99,102,241,0.35); color: var(--color-primary-hover); font-size: 0.8125rem; font-weight: 600; padding: 0.4rem 1rem; border-radius: 9999px; margin-bottom: 1.5rem; }
.hero h1 { font-size: clamp(2.25rem, 5vw, 3.5rem); font-weight: 800; line-height: 1.1; margin-bottom: 1.25rem; background: linear-gradient(135deg, #f1f5f9, #a5b4fc); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }
.hero-subtitle { font-size: 1.125rem; color: var(--color-text-muted); max-width: 580px; margin: 0 auto 2rem; line-height: 1.7; }
.hero-badges { display: flex; justify-content: center; gap: 0.75rem; flex-wrap: wrap; margin-bottom: 2rem; }
.hero-badge { display: flex; align-items: center; gap: 0.35rem; background: var(--color-surface); border: 1px solid var(--color-border); border-radius: 9999px; padding: 0.4rem 1rem; font-size: 0.8125rem; color: var(--color-text-muted); }
.hero-cta { display: flex; justify-content: center; gap: 1rem; flex-wrap: wrap; }

.index-content { max-width: 1100px; margin: 0 auto; padding: 3rem 2rem; }
.section-eyebrow { font-size: 0.6875rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.1em; color: var(--color-primary-hover); margin-bottom: 0.5rem; }
.section-title { font-size: 1.75rem; font-weight: 700; margin-bottom: 0.875rem; }
.section-desc { color: var(--color-text-muted); max-width: 580px; margin-bottom: 2rem; font-size: 1rem; line-height: 1.7; }

.stats-row { display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr)); gap: 1rem; margin-bottom: 3rem; }
.stat-card { background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: 1.25rem; text-align: center; }
.stat-value { font-size: 2rem; font-weight: 800; color: var(--color-primary-hover); margin-bottom: 0.25rem; }
.stat-label { font-size: 0.8rem; color: var(--color-text-muted); }

.modules-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 1rem; }
.module-card { background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-xl); padding: 1.375rem; text-decoration: none; transition: all var(--transition); display: flex; flex-direction: column; gap: 0.5rem; position: relative; overflow: hidden; }
.module-card:hover:not(.card-locked) { border-color: var(--color-primary); transform: translateY(-2px); box-shadow: var(--shadow-lg); }
.module-card.card-locked { opacity: 0.55; cursor: not-allowed; }
.module-card.card-completed { border-color: rgba(16,185,129,0.35); }
.module-card.card-active { border-color: var(--color-primary); }
.module-card-num { font-family: var(--font-mono); font-size: 0.6875rem; color: var(--color-text-dim); font-weight: 700; }
.module-card-title { font-size: 0.9375rem; font-weight: 600; color: var(--color-text); line-height: 1.3; }
.module-card-desc { font-size: 0.8rem; color: var(--color-text-muted); line-height: 1.5; flex: 1; }
.module-card-footer { display: flex; align-items: center; justify-content: space-between; margin-top: 0.5rem; padding-top: 0.625rem; border-top: 1px solid var(--color-border); }
.module-card-meta { display: flex; gap: 1rem; }
.module-card-meta span { font-size: 0.6875rem; color: var(--color-text-dim); display: flex; align-items: center; gap: 4px; }
.card-status-badge { font-size: 0.6875rem; font-weight: 700; padding: 2px 8px; border-radius: 9999px; }
.card-status-badge.completed { background: var(--color-success-dim); color: var(--color-success); }
.card-status-badge.locked { background: var(--color-surface-2); color: var(--color-text-dim); }
.card-status-badge.available { background: var(--color-primary-dim); color: var(--color-primary-hover); }

.prereqs-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 1rem; margin: 1.25rem 0; }
.prereq-item { background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: 1rem; display: flex; align-items: flex-start; gap: 0.625rem; }
.prereq-check { color: var(--color-success); font-size: 1rem; flex-shrink: 0; margin-top: 2px; }
.prereq-text { font-size: 0.8125rem; color: var(--color-text-muted); line-height: 1.5; }
.prereq-text strong { display: block; color: var(--color-text); margin-bottom: 2px; }

.tech-stack { display: flex; flex-wrap: wrap; gap: 0.625rem; margin: 1.25rem 0; }
.tech-badge { display: flex; align-items: center; gap: 0.35rem; background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-md); padding: 0.4rem 0.875rem; font-size: 0.8125rem; font-weight: 500; color: var(--color-text-muted); transition: all var(--transition); }
.tech-badge:hover { border-color: var(--color-primary); color: var(--color-primary-hover); }

.index-footer { background: var(--color-surface); border-top: 1px solid var(--color-border); padding: 1.5rem 2rem; text-align: center; font-size: 0.8125rem; color: var(--color-text-dim); }
.index-footer a { color: var(--color-text-muted); text-decoration: none; }
.index-footer a:hover { color: var(--color-primary-hover); }

/* ===== UTILITY ===== */
.hidden { display: none !important; }
.text-success { color: var(--color-success); }
.text-danger { color: var(--color-danger); }
.text-warning { color: var(--color-warning); }
.text-muted { color: var(--color-text-muted); }
.text-center { text-align: center; }
.mt-lg { margin-top: 2rem; }
.mb-lg { margin-bottom: 2rem; }
.badge { display: inline-flex; align-items: center; font-size: 0.6875rem; font-weight: 700; padding: 2px 8px; border-radius: 9999px; }
.badge-success { background: var(--color-success-dim); color: var(--color-success); }
.badge-danger { background: var(--color-danger-dim); color: var(--color-danger); }
.badge-warning { background: var(--color-warning-dim); color: var(--color-warning); }
.badge-info { background: var(--color-info-dim); color: var(--color-info); }

/* ===== ANIMATIONS ===== */
@keyframes fadeInUp { from { opacity: 0; transform: translateY(14px); } to { opacity: 1; transform: translateY(0); } }
.animate-in { animation: fadeInUp 0.35s ease forwards; }

/* ===== RESPONSIVE ===== */
@media (max-width: 1024px) {
  .sidebar { transform: translateX(-100%); }
  .sidebar.open { transform: translateX(0); box-shadow: var(--shadow-lg); }
  .main-wrapper { margin-left: 0; }
  .hamburger { display: block; }
}
@media (max-width: 768px) {
  .content { padding: 1.5rem 1.25rem; }
  .module-nav { padding: 1.25rem; }
  .card-grid { grid-template-columns: 1fr; }
  .modules-grid { grid-template-columns: 1fr; }
  .quiz-container { padding: 1.25rem; }
  .stats-row { grid-template-columns: repeat(2, 1fr); }
  .toc-list { columns: 1; }
  .module-header h1 { font-size: 1.625rem; }
  .index-content { padding: 2rem 1.25rem; }
  .hero { padding: 3.5rem 1.25rem; }
}