:root {
    --primary: #1a56db;
    --primary-dark: #1e3a8a;
    --primary-light: #dbeafe;
    --accent: #059669;
    --accent-light: #d1fae5;
    --orange: #ea580c;
    --orange-light: #fff7ed;
    --purple: #7c3aed;
    --purple-light: #ede9fe;
    --pink: #db2777;
    --pink-light: #fce7f3;
    --bg: #f8fafc;
    --card: #ffffff;
    --text: #1e293b;
    --text-light: #64748b;
    --border: #e2e8f0;
    --shadow: 0 1px 3px rgba(0,0,0,.1), 0 1px 2px rgba(0,0,0,.06);
    --shadow-lg: 0 10px 15px -3px rgba(0,0,0,.1), 0 4px 6px -2px rgba(0,0,0,.05);
    --radius: 12px;
}
* { margin:0; padding:0; box-sizing:border-box; }
body { font-family: 'Segoe UI', system-ui, -apple-system, sans-serif; background:var(--bg); color:var(--text); line-height:1.7; }

/* NAVBAR */
.navbar { background:var(--primary-dark); color:#fff; position:sticky; top:0; z-index:100; box-shadow:var(--shadow-lg); }
.navbar-inner { max-width:1200px; margin:0 auto; display:flex; align-items:center; justify-content:space-between; padding:0 24px; }
.navbar .logo { font-size:1.1rem; font-weight:700; padding:14px 0; }
.navbar .logo span { color:#93c5fd; }
.nav-links { display:flex; gap:4px; align-items:center; }
.nav-links a { color:#cbd5e1; text-decoration:none; padding:14px 14px; font-size:.85rem; font-weight:500; transition:all .2s; }
.nav-links a:hover { color:#fff; background:rgba(255,255,255,.1); }
.btn-back { display:inline-flex; align-items:center; gap:6px; background:rgba(255,255,255,.15); padding:8px 16px; border-radius:8px; color:#fff; text-decoration:none; font-size:.85rem; font-weight:600; transition:all .2s; }
.btn-back:hover { background:rgba(255,255,255,.25); }

/* HERO */
.lesson-hero { background:linear-gradient(135deg, var(--primary-dark), var(--primary)); padding:40px 24px; color:#fff; }
.lesson-hero-inner { max-width:1200px; margin:0 auto; }
.lesson-meta { display:flex; gap:8px; flex-wrap:wrap; margin-bottom:12px; }
.meta-badge { padding:4px 12px; border-radius:50px; font-size:.75rem; font-weight:600; }
.meta-badge.school { background:#93c5fd; color:var(--primary-dark); }
.meta-badge.class { background:#fbbf24; color:#78350f; }
.meta-badge.time { background:#34d399; color:#064e3b; }
.meta-badge.pp { background:#c4b5fd; color:#4c1d95; }
.lesson-hero h1 { font-size:1.8rem; font-weight:800; margin-bottom:8px; }
.lesson-hero .subtitle { color:#bfdbfe; font-size:1rem; }

/* MAIN */
.lesson-main { max-width:1200px; margin:0 auto; padding:24px; }

/* TIMELINE */
.timeline { display:flex; gap:8px; margin-bottom:32px; flex-wrap:wrap; }
.timeline-item { flex:1; min-width:120px; background:var(--card); border-radius:var(--radius); padding:12px 16px; box-shadow:var(--shadow); text-align:center; border-top:3px solid var(--border); }
.timeline-item.active { border-top-color:var(--primary); }
.timeline-item .t-time { font-size:.7rem; color:var(--text-light); font-weight:600; text-transform:uppercase; }
.timeline-item .t-label { font-size:.8rem; font-weight:700; color:var(--text); margin-top:2px; }
.timeline-item .t-min { font-size:.7rem; color:var(--primary); font-weight:600; }

/* SECTIONS */
.lesson-section { background:var(--card); border-radius:var(--radius); box-shadow:var(--shadow); margin-bottom:24px; overflow:hidden; }
.section-header { padding:20px 24px; display:flex; align-items:center; gap:12px; cursor:pointer; user-select:none; border-bottom:1px solid var(--border); }
.section-header:hover { background:#f8fafc; }
.section-icon { width:40px; height:40px; border-radius:10px; display:flex; align-items:center; justify-content:center; font-size:1.2rem; flex-shrink:0; }
.section-icon.theory { background:var(--primary-light); }
.section-icon.tasks { background:var(--orange-light); }
.section-icon.video { background:#fee2e2; }
.section-icon.podcast { background:var(--purple-light); }
.section-icon.game { background:var(--accent-light); }
.section-icon.pp { background:var(--pink-light); }
.section-header h2 { font-size:1.1rem; font-weight:700; flex:1; }
.section-header .chevron { font-size:1.2rem; color:var(--text-light); transition:transform .3s; }
.section-header.open .chevron { transform:rotate(180deg); }
.section-body { padding:24px; }

/* THEORY */
.theory-content h3 { font-size:1rem; font-weight:700; color:var(--primary-dark); margin:20px 0 8px; }
.theory-content h3:first-child { margin-top:0; }
.theory-content p { margin-bottom:12px; }
.theory-content ul, .theory-content ol { margin:8px 0 16px 24px; }
.theory-content li { margin-bottom:6px; }
.theory-content .highlight { background:var(--primary-light); border-left:4px solid var(--primary); padding:12px 16px; border-radius:0 8px 8px 0; margin:16px 0; }
.theory-content .warning { background:#fef3c7; border-left:4px solid #f59e0b; padding:12px 16px; border-radius:0 8px 8px 0; margin:16px 0; }
.theory-content code { background:#f1f5f9; padding:2px 6px; border-radius:4px; font-family:'Fira Code','Consolas',monospace; font-size:.88rem; }
.theory-content pre { background:#1e293b; color:#e2e8f0; padding:16px; border-radius:8px; overflow-x:auto; margin:12px 0; font-family:'Fira Code','Consolas',monospace; font-size:.85rem; line-height:1.6; }
.theory-content pre code { background:none; padding:0; color:inherit; }
.keyword { color:#60a5fa; }
.string { color:#34d399; }
.comment { color:#64748b; font-style:italic; }
.number { color:#fbbf24; }

/* TASKS */
.task-card { background:var(--bg); border-radius:8px; padding:16px; margin-bottom:12px; border-left:4px solid var(--orange); }
.task-card:last-child { margin-bottom:0; }
.task-card .task-level { font-size:.7rem; font-weight:700; text-transform:uppercase; letter-spacing:.5px; margin-bottom:4px; }
.task-card .task-level.easy { color:var(--accent); }
.task-card .task-level.medium { color:var(--orange); }
.task-card .task-level.hard { color:var(--pink); }
.task-card h4 { font-size:.95rem; margin-bottom:8px; }
.task-card p { font-size:.88rem; color:var(--text-light); }
.task-card .solution { margin-top:12px; }
.task-card .solution summary { cursor:pointer; color:var(--primary); font-weight:600; font-size:.85rem; }
.task-card .solution pre { margin-top:8px; }

/* VIDEO */
.video-grid { display:grid; grid-template-columns:repeat(auto-fill, minmax(320px, 1fr)); gap:16px; }
.video-card { background:var(--bg); border-radius:8px; overflow:hidden; }
.video-card iframe { width:100%; aspect-ratio:16/9; border:none; border-radius:8px 8px 0 0; }
.video-card .video-info { padding:12px; }
.video-card .video-title { font-size:.9rem; font-weight:700; margin-bottom:4px; }
.video-card .video-channel { font-size:.8rem; color:var(--text-light); }

/* PODCAST */
.podcast-list { display:flex; flex-direction:column; gap:12px; }
.podcast-item { display:flex; gap:16px; align-items:center; background:var(--bg); padding:16px; border-radius:8px; }
.podcast-icon { width:48px; height:48px; background:var(--purple-light); border-radius:12px; display:flex; align-items:center; justify-content:center; font-size:1.4rem; flex-shrink:0; }
.podcast-info h4 { font-size:.9rem; margin-bottom:2px; }
.podcast-info p { font-size:.8rem; color:var(--text-light); }
.podcast-info a { color:var(--purple); font-size:.8rem; font-weight:600; text-decoration:none; }

/* GAME */
.game-grid { display:grid; grid-template-columns:repeat(auto-fill, minmax(280px, 1fr)); gap:16px; }
.game-card { background:var(--bg); border-radius:8px; padding:20px; text-align:center; border:2px solid var(--border); transition:all .2s; }
.game-card:hover { border-color:var(--accent); transform:translateY(-2px); box-shadow:var(--shadow-lg); }
.game-card .game-icon { font-size:2rem; margin-bottom:8px; }
.game-card h4 { font-size:.95rem; margin-bottom:6px; }
.game-card p { font-size:.8rem; color:var(--text-light); margin-bottom:12px; }
.game-card a { display:inline-block; background:var(--accent); color:#fff; padding:8px 20px; border-radius:50px; font-size:.8rem; font-weight:600; text-decoration:none; transition:all .2s; }
.game-card a:hover { background:#047857; }

/* PP REF */
.pp-ref-box { background:var(--bg); border-radius:8px; padding:16px; border-left:4px solid var(--pink); }
.pp-ref-box .pp-label { font-size:.75rem; font-weight:700; text-transform:uppercase; color:var(--pink); margin-bottom:8px; }
.pp-ref-box .pp-content { font-size:.88rem; }
.pp-ref-box .pp-page { font-size:.75rem; color:var(--text-light); margin-top:4px; }

/* LESSON TAGS */
.lesson-tags { display:flex; flex-wrap:wrap; gap:6px; margin-top:12px; }
.lesson-tag { display:inline-block; padding:3px 10px; background:rgba(255,255,255,.12); border:1px solid rgba(255,255,255,.22); border-radius:20px; color:rgba(255,255,255,.85); font-size:.72rem; letter-spacing:.3px; transition:all .2s; cursor:default; }
.lesson-tag:hover { background:rgba(255,255,255,.22); color:#fff; }

/* PP LINK & MODAL */
.pp-link { display:inline-block; margin-top:10px; padding:6px 14px; background:rgba(255,255,255,.15); border:1px solid rgba(255,255,255,.3); border-radius:6px; color:#fff; font-size:.82rem; text-decoration:none; cursor:pointer; transition:all .2s; backdrop-filter:blur(4px); }
.pp-link:hover { background:rgba(255,255,255,.25); border-color:rgba(255,255,255,.5); }
.pp-modal-overlay { display:none; position:fixed; inset:0; background:rgba(0,0,0,.7); z-index:9999; align-items:center; justify-content:center; }
.pp-modal-overlay.open { display:flex; }
.pp-modal { background:#fff; border-radius:12px; width:95vw; height:92vh; max-width:1200px; display:flex; flex-direction:column; overflow:hidden; box-shadow:0 20px 60px rgba(0,0,0,.4); }
.pp-modal-header { display:flex; align-items:center; justify-content:space-between; padding:14px 20px; border-bottom:1px solid #e5e7eb; background:#f9fafb; }
.pp-modal-header h3 { font-size:.95rem; color:#1e293b; margin:0; }
.pp-modal-close { background:none; border:none; font-size:1.5rem; cursor:pointer; color:#64748b; padding:4px 8px; border-radius:4px; line-height:1; }
.pp-modal-close:hover { background:#f1f5f9; color:#1e293b; }
.pp-modal-body { display:flex; flex:1; min-height:0; }
.pp-modal-pdf { flex:1; min-width:0; }
.pp-modal-pdf iframe { width:100%; height:100%; border:none; }
.pp-modal-sidebar { width:340px; border-left:1px solid #e5e7eb; padding:20px; overflow-y:auto; background:#fffbeb; }
.pp-modal-sidebar h4 { font-size:.8rem; text-transform:uppercase; color:#92400e; margin:0 0 12px; font-weight:700; letter-spacing:.5px; }
.pp-highlight { background:#fef08a; padding:14px; border-radius:8px; font-size:.85rem; line-height:1.6; color:#1e293b; border-left:4px solid #eab308; }
.pp-modal-sidebar .pp-source { font-size:.7rem; color:#a16207; margin-top:14px; font-style:italic; }
@media(max-width:768px) { .pp-modal-body { flex-direction:column; } .pp-modal-sidebar { width:100%; max-height:200px; border-left:none; border-top:1px solid #e5e7eb; } }

/* NAV BOTTOM */
.lesson-nav { display:flex; justify-content:space-between; margin-top:32px; gap:16px; flex-wrap:wrap; }
.lesson-nav a { display:inline-flex; align-items:center; gap:8px; padding:12px 24px; background:var(--card); border:2px solid var(--border); border-radius:var(--radius); text-decoration:none; color:var(--text); font-weight:600; font-size:.9rem; transition:all .2s; box-shadow:var(--shadow); }
.lesson-nav a:hover { border-color:var(--primary); color:var(--primary); }

/* FOOTER */
.lesson-footer { background:var(--primary-dark); color:#94a3b8; padding:24px; text-align:center; margin-top:48px; font-size:.8rem; }
.lesson-footer strong { color:#fff; }

/* LOCAL VIDEO */
.video-card .lesson-video { width:100%; aspect-ratio:16/9; border-radius:8px 8px 0 0; background:#000; }

/* QUIZ */
.quiz-container { display:flex; flex-direction:column; gap:20px; }
.quiz-question { background:var(--bg); border-radius:8px; padding:20px; border-left:4px solid var(--accent); }
.quiz-question h4 { font-size:.95rem; margin-bottom:12px; color:var(--text); }
.quiz-option { display:block; width:100%; text-align:left; padding:10px 16px; margin-bottom:8px; background:var(--card); border:2px solid var(--border); border-radius:8px; font-size:.88rem; font-family:inherit; cursor:pointer; transition:all .2s; color:var(--text); }
.quiz-option:hover { border-color:var(--primary); background:var(--primary-light); }
.quiz-option.correct { border-color:var(--accent); background:var(--accent-light); color:#064e3b; font-weight:600; }
.quiz-option.incorrect { border-color:#ef4444; background:#fef2f2; color:#991b1b; }
.quiz-option:disabled { cursor:default; opacity:.7; }
.quiz-option:disabled:hover { border-color:var(--border); background:var(--card); }
.quiz-option:disabled.correct:hover { border-color:var(--accent); background:var(--accent-light); }
.quiz-option:disabled.incorrect:hover { border-color:#ef4444; background:#fef2f2; }
.quiz-feedback { margin-top:8px; padding:10px 14px; border-radius:6px; font-size:.85rem; display:none; }
.quiz-feedback.show { display:block; }
.quiz-feedback.correct { background:var(--accent-light); color:#064e3b; border-left:3px solid var(--accent); }
.quiz-feedback.incorrect { background:#fef2f2; color:#991b1b; border-left:3px solid #ef4444; }
.quiz-score { text-align:center; padding:16px; background:var(--primary-light); border-radius:8px; font-weight:700; color:var(--primary-dark); font-size:1rem; margin-top:8px; }

/* OFFLINE PODCAST */
.podcast-info .offline-note { display:block; margin-top:6px; font-size:.75rem; color:var(--text-light); font-style:italic; }

/* RESPONSIVE */
@media(max-width:768px) {
    .navbar-inner { flex-direction:column; padding:12px; gap:8px; }
    .lesson-hero h1 { font-size:1.3rem; }
    .timeline { flex-direction:column; }
    .video-grid { grid-template-columns:1fr; }
    .game-grid { grid-template-columns:1fr; }
    .section-body { padding:16px; }
}