/* ===== CSS VARIABLES & THEME ===== */
:root {
  --bg: #0a0e14;
  --surface: #111822;
  --surface-2: #182030;
  --surface-3: #1f2a3e;
  --border: #2a3650;
  --text: #e2e8f0;
  --text-muted: #94a3b8;
  --text-faint: #64748b;
  --primary: #336791;
  --primary-hover: #2a5578;
  --primary-glow: rgba(51, 103, 145, 0.3);
  --secondary: #4a90d9;
  --secondary-glow: rgba(74, 144, 217, 0.2);
  --success: #10b981;
  --error: #ef4444;
  --warning: #f59e0b;
  --code-bg: #0c1017;
  --code-border: #1e2c42;
  --sidebar-w: 300px;
  --topbar-h: 60px;
  --font-body: 'Inter', system-ui, -apple-system, sans-serif;
  --font-code: 'JetBrains Mono', 'Fira Code', monospace;
  --radius: 10px;
  --radius-sm: 6px;
}

[data-theme="light"] {
  --bg: #f5f7fa;
  --surface: #ffffff;
  --surface-2: #eef1f6;
  --surface-3: #e2e7f0;
  --border: #cbd5e1;
  --text: #1e293b;
  --text-muted: #475569;
  --text-faint: #94a3b8;
  --code-bg: #f0f3f8;
  --code-border: #d1d9e6;
  --primary-glow: rgba(51, 103, 145, 0.12);
  --secondary-glow: rgba(74, 144, 217, 0.1);
}

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

html { scroll-behavior: smooth; font-size: 16px; -webkit-text-size-adjust: 100%; }

body {
  font-family: var(--font-body);
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  overflow-x: hidden;
  transition: background 0.3s, color 0.3s;
}

::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-faint); }

.topbar {
  position: fixed; top: 0; left: 0; right: 0;
  height: var(--topbar-h);
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  display: flex; align-items: center;
  padding: 0 20px; z-index: 100; gap: 16px;
  backdrop-filter: blur(12px);
}

.topbar-logo {
  display: flex; align-items: center; gap: 10px;
  font-weight: 700; font-size: 1.1rem;
  color: var(--text); white-space: nowrap; flex-shrink: 0;
}
.topbar-logo svg { flex-shrink: 0; }
.topbar-logo .logo-accent { color: var(--primary); }

.hamburger {
  display: none; background: none; border: none;
  color: var(--text); cursor: pointer; padding: 4px; flex-shrink: 0;
}

.topbar-center { flex: 1; display: flex; align-items: center; justify-content: center; gap: 16px; min-width: 0; }

.xp-display { display: flex; align-items: center; gap: 10px; font-size: 0.85rem; font-weight: 600; white-space: nowrap; }

.xp-bar-container { width: 180px; height: 8px; background: var(--surface-2); border-radius: 4px; overflow: hidden; position: relative; }

.xp-bar-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--secondary));
  border-radius: 4px;
  transition: width 0.6s cubic-bezier(0.22, 1, 0.36, 1);
  position: relative;
}
.xp-bar-fill::after {
  content: ''; position: absolute; right: 0; top: 0; bottom: 0; width: 20px;
  background: linear-gradient(90deg, transparent, rgba(255,255,255,0.3));
  animation: xpShimmer 2s infinite;
}
@keyframes xpShimmer { 0%, 100% { opacity: 0; } 50% { opacity: 1; } }

.level-badge {
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  color: #fff; padding: 3px 10px; border-radius: 12px;
  font-size: 0.75rem; font-weight: 700; white-space: nowrap;
  text-transform: uppercase; letter-spacing: 0.03em;
}

.topbar-actions { display: flex; align-items: center; gap: 8px; flex-shrink: 0; }

.topbar-btn {
  background: var(--surface-2); border: 1px solid var(--border);
  color: var(--text-muted); padding: 6px 12px; border-radius: var(--radius-sm);
  cursor: pointer; font-size: 0.8rem; font-family: var(--font-body);
  display: flex; align-items: center; gap: 6px; transition: all 0.2s; white-space: nowrap;
}
.topbar-btn:hover { background: var(--surface-3); color: var(--text); border-color: var(--primary); }
.topbar-btn kbd { font-family: var(--font-body); font-size: 0.7rem; background: var(--bg); padding: 1px 5px; border-radius: 3px; border: 1px solid var(--border); }

/* ===== SIDEBAR ===== */
.sidebar {
  position: fixed; top: var(--topbar-h); left: 0;
  width: var(--sidebar-w); height: calc(100vh - var(--topbar-h));
  background: var(--surface); border-right: 1px solid var(--border);
  overflow-y: auto; z-index: 90; padding: 16px 0;
  transition: transform 0.3s cubic-bezier(0.22, 1, 0.36, 1);
}
.sidebar-overlay { display: none; position: fixed; inset: 0; background: rgba(0,0,0,0.5); z-index: 89; }

.overall-progress { padding: 0 16px 16px; border-bottom: 1px solid var(--border); margin-bottom: 8px; }
.overall-progress-label { font-size: 0.75rem; color: var(--text-muted); margin-bottom: 6px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.05em; }
.overall-bar { width: 100%; height: 6px; background: var(--surface-2); border-radius: 3px; overflow: hidden; }
.overall-bar-fill { height: 100%; background: linear-gradient(90deg, var(--primary), var(--success)); border-radius: 3px; transition: width 0.5s; }
.overall-pct { font-size: 0.75rem; color: var(--text-muted); margin-top: 4px; text-align: right; }

.track-nav-item { padding: 10px 16px; cursor: pointer; transition: background 0.15s; border-left: 3px solid transparent; }
.track-nav-item:hover { background: var(--surface-2); }
.track-nav-item.active { background: var(--surface-2); border-left-color: var(--primary); }

.track-nav-header { display: flex; align-items: center; gap: 8px; font-size: 0.85rem; font-weight: 600; color: var(--text); margin-bottom: 6px; }
.track-nav-header .track-icon { font-size: 1rem; }

.track-progress-bar { width: 100%; height: 4px; background: var(--surface-3); border-radius: 2px; overflow: hidden; }
.track-progress-fill { height: 100%; background: var(--primary); border-radius: 2px; transition: width 0.4s; }
.track-progress-text { font-size: 0.7rem; color: var(--text-faint); margin-top: 3px; }

.track-lessons { max-height: 0; overflow: hidden; transition: max-height 0.3s; }
.track-nav-item.active .track-lessons { max-height: 800px; }

.lesson-nav-item { padding: 5px 16px 5px 32px; font-size: 0.8rem; color: var(--text-muted); cursor: pointer; display: flex; align-items: center; gap: 8px; transition: color 0.15s; }
.lesson-nav-item:hover { color: var(--text); }
.lesson-nav-item.current { color: var(--primary); font-weight: 600; }
.lesson-nav-item.completed { color: var(--success); }

.lesson-nav-check { width: 14px; height: 14px; border: 1.5px solid var(--border); border-radius: 50%; flex-shrink: 0; display: flex; align-items: center; justify-content: center; font-size: 0.6rem; }
.lesson-nav-item.completed .lesson-nav-check { background: var(--success); border-color: var(--success); color: #fff; }
.lesson-nav-item.current .lesson-nav-check { border-color: var(--primary); }

.sidebar-quiz-btn { display: block; margin: 8px 16px 8px 32px; padding: 5px 12px; background: var(--surface-3); border: 1px solid var(--border); color: var(--text-muted); border-radius: var(--radius-sm); font-size: 0.75rem; cursor: pointer; transition: all 0.2s; text-align: center; font-family: var(--font-body); }
.sidebar-quiz-btn:hover { border-color: var(--primary); color: var(--primary); }
.sidebar-quiz-btn.completed { background: var(--success); color: #fff; border-color: var(--success); }

/* ===== MAIN CONTENT ===== */
.main { margin-left: var(--sidebar-w); margin-top: var(--topbar-h); min-height: calc(100vh - var(--topbar-h)); padding: 40px 48px; max-width: 900px; }

.lesson-header { margin-bottom: 32px; }
.lesson-breadcrumb { font-size: 0.8rem; color: var(--text-faint); margin-bottom: 8px; }
.lesson-breadcrumb span { color: var(--primary); }
.lesson-title { font-size: 1.8rem; font-weight: 800; line-height: 1.2; margin-bottom: 8px; background: linear-gradient(135deg, var(--text), var(--secondary)); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }
.lesson-meta { font-size: 0.8rem; color: var(--text-faint); display: flex; gap: 16px; }

.lesson-content h2 { font-size: 1.3rem; font-weight: 700; margin: 32px 0 12px; color: var(--text); }
.lesson-content h3 { font-size: 1.1rem; font-weight: 600; margin: 24px 0 10px; color: var(--text); }
.lesson-content p { margin-bottom: 16px; color: var(--text); line-height: 1.7; }
.lesson-content ul, .lesson-content ol { margin-bottom: 16px; padding-left: 24px; }
.lesson-content li { margin-bottom: 6px; line-height: 1.6; }
.lesson-content strong { color: var(--secondary); font-weight: 600; }
.lesson-content em { color: var(--primary); font-style: normal; }

.inline-code { font-family: var(--font-code); font-size: 0.85em; background: var(--code-bg); border: 1px solid var(--code-border); padding: 1px 6px; border-radius: 4px; color: var(--secondary); }

.code-block { position: relative; margin: 16px 0 24px; border-radius: var(--radius); border: 1px solid var(--code-border); overflow: hidden; }
.code-block-header { display: flex; align-items: center; justify-content: space-between; padding: 6px 14px; background: var(--surface-2); border-bottom: 1px solid var(--code-border); font-size: 0.75rem; }
.code-lang { color: var(--text-faint); font-family: var(--font-code); font-weight: 600; text-transform: uppercase; letter-spacing: 0.05em; }

.copy-btn { background: none; border: 1px solid var(--border); color: var(--text-muted); padding: 3px 10px; border-radius: 4px; cursor: pointer; font-size: 0.72rem; font-family: var(--font-body); transition: all 0.2s; }
.copy-btn:hover { color: var(--text); border-color: var(--primary); }
.copy-btn.copied { color: var(--success); border-color: var(--success); }

.code-block pre { padding: 16px; overflow-x: auto; background: var(--code-bg); font-family: var(--font-code); font-size: 0.84rem; line-height: 1.6; tab-size: 2; color: var(--text); }

.tok-kw { color: #c678dd; }
.tok-str { color: #98c379; }
.tok-num { color: #d19a66; }
.tok-cm { color: #5c6370; font-style: italic; }
.tok-fn { color: #61afef; }
.tok-op { color: #56b6c2; }
.tok-type { color: #e5c07b; }
.tok-dec { color: #c678dd; }
.tok-prop { color: #e06c75; }
.tok-punc { color: #abb2bf; }

.info-box { padding: 16px 20px; border-radius: var(--radius); margin: 20px 0; border-left: 4px solid; font-size: 0.9rem; }
.info-box.tip { background: rgba(16, 185, 129, 0.08); border-color: var(--success); }
.info-box.warning { background: rgba(245, 158, 11, 0.08); border-color: var(--warning); }
.info-box.info { background: rgba(51, 103, 145, 0.08); border-color: var(--primary); }
.info-box.danger { background: rgba(239, 68, 68, 0.08); border-color: var(--error); }
.info-box-title { font-weight: 700; margin-bottom: 4px; font-size: 0.85rem; }
.info-box.tip .info-box-title { color: var(--success); }
.info-box.warning .info-box-title { color: var(--warning); }
.info-box.info .info-box-title { color: var(--primary); }
.info-box.danger .info-box-title { color: var(--error); }

.takeaways { background: var(--surface-2); border: 1px solid var(--border); border-radius: var(--radius); padding: 20px 24px; margin: 28px 0; }
.takeaways-title { font-size: 0.85rem; font-weight: 700; color: var(--primary); text-transform: uppercase; letter-spacing: 0.05em; margin-bottom: 10px; }
.takeaways ul { padding-left: 18px; }
.takeaways li { margin-bottom: 4px; font-size: 0.9rem; }

.lesson-content table { width: 100%; border-collapse: collapse; margin: 16px 0 24px; font-size: 0.88rem; }
.lesson-content th { background: var(--surface-2); padding: 10px 14px; text-align: left; font-weight: 600; border: 1px solid var(--border); font-size: 0.82rem; text-transform: uppercase; letter-spacing: 0.03em; color: var(--text-muted); }
.lesson-content td { padding: 10px 14px; border: 1px solid var(--border); vertical-align: top; }

.lesson-complete-btn { display: inline-flex; align-items: center; gap: 8px; padding: 12px 28px; background: linear-gradient(135deg, var(--primary), var(--primary-hover)); color: #fff; border: none; border-radius: var(--radius); font-size: 0.95rem; font-weight: 600; cursor: pointer; margin-top: 32px; font-family: var(--font-body); transition: all 0.3s; box-shadow: 0 4px 15px var(--primary-glow); }
.lesson-complete-btn:hover { transform: translateY(-2px); box-shadow: 0 6px 25px var(--primary-glow); }
.lesson-complete-btn.completed { background: var(--success); box-shadow: none; cursor: default; }
.lesson-complete-btn.completed:hover { transform: none; }

.lesson-nav { display: flex; justify-content: space-between; margin-top: 24px; padding-top: 24px; border-top: 1px solid var(--border); }
.lesson-nav-btn { padding: 8px 16px; background: var(--surface-2); border: 1px solid var(--border); color: var(--text-muted); border-radius: var(--radius-sm); cursor: pointer; font-size: 0.85rem; font-family: var(--font-body); transition: all 0.2s; }
.lesson-nav-btn:hover { border-color: var(--primary); color: var(--text); }
.lesson-nav-btn:disabled { opacity: 0.3; cursor: default; }
.lesson-nav-btn:disabled:hover { border-color: var(--border); color: var(--text-muted); }

/* ===== QUIZ ===== */
.quiz-container { margin: 24px 0; }
.quiz-question { background: var(--surface-2); border: 1px solid var(--border); border-radius: var(--radius); padding: 20px 24px; margin-bottom: 20px; }
.quiz-question-text { font-weight: 600; margin-bottom: 14px; font-size: 1rem; }
.quiz-option { display: block; width: 100%; text-align: left; padding: 10px 16px; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius-sm); color: var(--text); cursor: pointer; margin-bottom: 8px; font-size: 0.9rem; font-family: var(--font-body); transition: all 0.2s; }
.quiz-option:hover:not(.selected) { border-color: var(--primary); background: var(--surface-3); }
.quiz-option.correct { border-color: var(--success); background: rgba(16,185,129,0.1); color: var(--success); }
.quiz-option.incorrect { border-color: var(--error); background: rgba(239,68,68,0.1); color: var(--error); }
.quiz-option.show-correct { border-color: var(--success); background: rgba(16,185,129,0.08); }
.quiz-explanation { margin-top: 8px; padding: 10px 14px; background: var(--surface-3); border-radius: var(--radius-sm); font-size: 0.85rem; color: var(--text-muted); display: none; }
.quiz-explanation.visible { display: block; }
.quiz-score { text-align: center; padding: 24px; font-size: 1.2rem; font-weight: 700; }

/* ===== SEARCH MODAL ===== */
.search-overlay { display: none; position: fixed; inset: 0; background: rgba(0,0,0,0.6); z-index: 200; justify-content: center; padding-top: 15vh; backdrop-filter: blur(4px); }
.search-overlay.open { display: flex; }
.search-modal { width: 560px; max-width: 90vw; max-height: 60vh; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); box-shadow: 0 20px 60px rgba(0,0,0,0.4); overflow: hidden; display: flex; flex-direction: column; }
.search-input-wrap { display: flex; align-items: center; padding: 14px 18px; border-bottom: 1px solid var(--border); gap: 10px; }
.search-input-wrap svg { color: var(--text-muted); flex-shrink: 0; }
.search-input { flex: 1; background: none; border: none; color: var(--text); font-size: 1rem; font-family: var(--font-body); outline: none; }
.search-input::placeholder { color: var(--text-faint); }
.search-results { overflow-y: auto; max-height: 400px; }
.search-result-item { padding: 12px 18px; cursor: pointer; border-bottom: 1px solid var(--border); transition: background 0.1s; }
.search-result-item:hover { background: var(--surface-2); }
.search-result-track { font-size: 0.72rem; color: var(--primary); font-weight: 600; text-transform: uppercase; letter-spacing: 0.05em; }
.search-result-title { font-size: 0.9rem; font-weight: 500; color: var(--text); }
.search-empty { padding: 32px; text-align: center; color: var(--text-faint); font-size: 0.9rem; }

/* ===== ACHIEVEMENTS PANEL ===== */
.achievements-btn { position: fixed; bottom: 24px; right: 24px; width: 52px; height: 52px; background: linear-gradient(135deg, var(--primary), var(--secondary)); border: none; border-radius: 50%; color: #fff; font-size: 1.4rem; cursor: pointer; z-index: 80; box-shadow: 0 4px 20px var(--primary-glow); transition: transform 0.2s; display: flex; align-items: center; justify-content: center; }
.achievements-btn:hover { transform: scale(1.1); }
.achievements-panel { display: none; position: fixed; bottom: 90px; right: 24px; width: 340px; max-height: 70vh; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); box-shadow: 0 10px 40px rgba(0,0,0,0.3); z-index: 80; overflow-y: auto; padding: 20px; }
.achievements-panel.open { display: block; }
.achievements-panel h3 { font-size: 1rem; font-weight: 700; margin-bottom: 16px; color: var(--text); }
.achievement-item { display: flex; align-items: center; gap: 12px; padding: 10px 0; border-bottom: 1px solid var(--border); }
.achievement-item:last-child { border-bottom: none; }
.achievement-icon { width: 36px; height: 36px; border-radius: 50%; display: flex; align-items: center; justify-content: center; font-size: 1.1rem; background: var(--surface-2); flex-shrink: 0; }
.achievement-item.unlocked .achievement-icon { background: linear-gradient(135deg, var(--primary), var(--secondary)); }
.achievement-name { font-weight: 600; font-size: 0.85rem; color: var(--text); }
.achievement-desc { font-size: 0.75rem; color: var(--text-muted); }
.achievement-item:not(.unlocked) { opacity: 0.4; }

/* ===== TOAST ===== */
.toast-container { position: fixed; top: 80px; right: 20px; z-index: 300; display: flex; flex-direction: column; gap: 10px; }
.toast { background: var(--surface); border: 1px solid var(--primary); border-radius: var(--radius); padding: 14px 20px; box-shadow: 0 8px 30px rgba(0,0,0,0.3); display: flex; align-items: center; gap: 10px; animation: toastIn 0.4s cubic-bezier(0.22, 1, 0.36, 1); max-width: 340px; }
.toast.exit { animation: toastOut 0.3s forwards; }
@keyframes toastIn { from { transform: translateX(120%); opacity: 0; } to { transform: translateX(0); opacity: 1; } }
@keyframes toastOut { to { transform: translateX(120%); opacity: 0; } }
.toast-icon { font-size: 1.2rem; }
.toast-text { font-size: 0.85rem; font-weight: 500; }

/* ===== LEVEL UP MODAL ===== */
.levelup-overlay { display: none; position: fixed; inset: 0; background: rgba(0,0,0,0.7); z-index: 400; justify-content: center; align-items: center; backdrop-filter: blur(6px); }
.levelup-overlay.open { display: flex; }
.levelup-modal { background: var(--surface); border: 2px solid var(--primary); border-radius: 16px; padding: 40px 50px; text-align: center; box-shadow: 0 0 80px var(--primary-glow); animation: levelPop 0.5s cubic-bezier(0.22, 1, 0.36, 1); max-width: 90vw; }
@keyframes levelPop { from { transform: scale(0.5); opacity: 0; } to { transform: scale(1); opacity: 1; } }
.levelup-emoji { font-size: 4rem; margin-bottom: 16px; display: block; }
.levelup-title { font-size: 1.6rem; font-weight: 800; color: var(--primary); margin-bottom: 8px; }
.levelup-subtitle { color: var(--text-muted); font-size: 0.95rem; margin-bottom: 24px; }
.levelup-close { padding: 10px 32px; background: var(--primary); color: #fff; border: none; border-radius: var(--radius-sm); font-size: 0.95rem; font-weight: 600; cursor: pointer; font-family: var(--font-body); }

#confetti-canvas { position: fixed; inset: 0; z-index: 500; pointer-events: none; }

/* ===== WELCOME SCREEN ===== */
.welcome { text-align: center; padding: 60px 20px; max-width: 650px; margin: 0 auto; }
.welcome h1 { font-size: 2.4rem; font-weight: 800; margin-bottom: 16px; background: linear-gradient(135deg, var(--primary), var(--secondary)); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }
.welcome p { color: var(--text-muted); font-size: 1.05rem; line-height: 1.7; margin-bottom: 32px; }
.welcome-tracks { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; text-align: left; }
.welcome-track-card { background: var(--surface-2); border: 1px solid var(--border); border-radius: var(--radius); padding: 16px; cursor: pointer; transition: all 0.2s; }
.welcome-track-card:hover { border-color: var(--primary); transform: translateY(-2px); }
.welcome-track-card .track-num { font-size: 0.7rem; color: var(--primary); font-weight: 700; text-transform: uppercase; letter-spacing: 0.08em; }
.welcome-track-card .track-name { font-weight: 600; font-size: 0.9rem; margin-top: 2px; }

.ascii-diagram { font-family: var(--font-code); font-size: 0.78rem; line-height: 1.4; background: var(--code-bg); border: 1px solid var(--code-border); border-radius: var(--radius); padding: 16px; overflow-x: auto; white-space: pre; margin: 16px 0; color: var(--secondary); }

/* ===== RESPONSIVE ===== */
@media (max-width: 768px) {
  .hamburger { display: flex; }
  .sidebar { transform: translateX(-100%); width: 280px; }
  .sidebar.open { transform: translateX(0); }
  .sidebar-overlay.open { display: block; }
  .main { margin-left: 0; padding: 24px 18px; }
  .topbar-btn kbd { display: none; }
  .xp-bar-container { width: 100px; }
  .welcome-tracks { grid-template-columns: 1fr; }
  .lesson-title { font-size: 1.4rem; }
  .welcome h1 { font-size: 1.8rem; }
  .achievements-panel { right: 10px; left: 10px; width: auto; bottom: 84px; }
  .achievements-btn { bottom: 16px; right: 16px; width: 46px; height: 46px; }
}
@media (max-width: 480px) {
  .topbar { padding: 0 12px; gap: 8px; }
  .topbar-logo span { display: none; }
  .level-badge { font-size: 0.65rem; padding: 2px 8px; }
  .main { padding: 16px 14px; }
}