*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }
:root {
  --bg: #0a0e1a;
  --bg-card: rgba(255,255,255,0.04);
  --bg-card-hover: rgba(255,255,255,0.07);
  --text: #f0f2f8;
  --text-sec: #9ba3b8;
  --text-muted: #6b7280;
  --accent: #4f8cff;
  --accent2: #a78bfa;
  --teal: #2dd4bf;
  --rose: #fb7185;
  --amber: #fbbf24;
  --border: rgba(255,255,255,0.06);
  --radius: 18px;
  --font: 'Inter', sans-serif;
  --font-d: 'Space Grotesk', sans-serif;
}
html { scroll-behavior: smooth; }
body {
  font-family: var(--font);
  background: var(--bg); color: var(--text);
  min-height: 100vh; overflow-x: hidden; line-height: 1.7;
}
.bg-glow {
  position: fixed; inset: 0; z-index: 0; pointer-events: none;
  background:
    radial-gradient(ellipse 600px 400px at 15% 5%, rgba(79,140,255,0.14), transparent),
    radial-gradient(ellipse 500px 350px at 85% 75%, rgba(167,139,250,0.10), transparent);
}
.container { position: relative; z-index: 1; max-width: 820px; margin: 0 auto; padding: 2rem 1.5rem; }

/* Top nav */
.top-nav {
  display: flex; align-items: center; justify-content: space-between;
  padding: 1rem 0; margin-bottom: 2rem;
  border-bottom: 1px solid var(--border);
  animation: fadeIn 0.6s ease;
}
.back-link {
  display: inline-flex; align-items: center; gap: 0.5rem;
  color: var(--text-sec); text-decoration: none; font-size: 0.88rem; font-weight: 500;
  transition: color 0.3s;
}
.back-link:hover { color: var(--accent); }
.nav-progress { font-size: 0.78rem; color: var(--text-muted); font-weight: 600; }

/* Module header */
.mod-header { text-align: center; padding: 2rem 0 3rem; animation: fadeInDown 0.8s ease; }
.mod-badge {
  display: inline-flex; align-items: center; gap: 0.5rem;
  padding: 0.45rem 1rem; border-radius: 100px;
  background: rgba(79,140,255,0.1); border: 1px solid rgba(79,140,255,0.2);
  font-size: 0.75rem; font-weight: 700; color: var(--accent);
  letter-spacing: 0.06em; text-transform: uppercase; margin-bottom: 1.2rem;
}
.mod-title {
  font-family: var(--font-d);
  font-size: clamp(1.8rem, 4vw, 2.6rem);
  font-weight: 700; line-height: 1.2; margin-bottom: 0.8rem;
  background: linear-gradient(135deg, #f0f2f8 20%, #4f8cff 60%, #a78bfa 100%);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.mod-subtitle { font-size: 1.05rem; color: var(--text-sec); max-width: 560px; margin: 0 auto; }

/* Objectives */
.objectives {
  background: linear-gradient(135deg, rgba(79,140,255,0.08), rgba(167,139,250,0.06));
  border: 1px solid rgba(79,140,255,0.12);
  border-radius: var(--radius); padding: 1.8rem 2rem; margin-bottom: 2.5rem;
  animation: fadeInUp 1s ease;
}
.objectives h3 { font-family: var(--font-d); font-size: 1rem; font-weight: 700; margin-bottom: 1rem; color: var(--accent); }
.objectives ul { list-style: none; }
.objectives li { position: relative; padding-left: 1.6rem; margin-bottom: 0.6rem; font-size: 0.92rem; color: var(--text-sec); }
.objectives li::before { content: '✦'; position: absolute; left: 0; color: var(--accent2); }

/* Lesson card */
.lesson {
  background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius);
  margin-bottom: 1.5rem; overflow: hidden; transition: all 0.3s ease;
  animation: fadeInUp calc(1s + var(--i,0) * 0.12s) ease backwards;
}
.lesson:hover { border-color: rgba(255,255,255,0.1); box-shadow: 0 8px 30px rgba(0,0,0,0.2); }
.lesson-header {
  display: flex; align-items: center; gap: 1rem;
  padding: 1.4rem 1.8rem; cursor: pointer; user-select: none; transition: background 0.2s;
}
.lesson-header:hover { background: var(--bg-card-hover); }
.lesson-num {
  width: 36px; height: 36px; border-radius: 10px;
  display: flex; align-items: center; justify-content: center;
  font-family: var(--font-d); font-weight: 700; font-size: 0.85rem;
  background: rgba(79,140,255,0.12); color: var(--accent); flex-shrink: 0;
}
.lesson-num.completed { background: rgba(45,212,191,0.15); color: var(--teal); }
.lesson-info { flex: 1; }
.lesson-name { font-weight: 600; font-size: 1rem; margin-bottom: 0.15rem; }
.lesson-time { font-size: 0.78rem; color: var(--text-muted); }
.lesson-toggle { font-size: 1.2rem; color: var(--text-muted); transition: transform 0.3s; }
.lesson.open .lesson-toggle { transform: rotate(180deg); }
.lesson-body { max-height: 0; overflow: hidden; transition: max-height 0.5s cubic-bezier(0.25,0.46,0.45,0.94); }
.lesson.open .lesson-body { max-height: 5000px; }
.lesson-content { padding: 0 1.8rem 1.8rem; border-top: 1px solid var(--border); }
.lesson-content h4 {
  font-family: var(--font-d); font-size: 0.95rem; font-weight: 700;
  margin: 1.4rem 0 0.7rem; color: var(--accent2);
}
.lesson-content p, .lesson-content li { font-size: 0.92rem; color: var(--text-sec); line-height: 1.75; }
.lesson-content ul { padding-left: 1.2rem; margin-bottom: 0.8rem; }
.lesson-content li { margin-bottom: 0.4rem; }
.lesson-content code {
  background: rgba(79,140,255,0.1); padding: 0.15rem 0.45rem; border-radius: 6px;
  font-size: 0.85rem; color: var(--accent);
}

/* Key concept, activity, tip boxes */
.key-concept {
  background: rgba(45,212,191,0.06); border-left: 3px solid var(--teal);
  border-radius: 0 12px 12px 0; padding: 1rem 1.2rem; margin: 1rem 0;
}
.key-concept strong { color: var(--teal); }
.key-concept p { font-size: 0.88rem; }
.activity-box {
  background: rgba(251,113,133,0.06); border-left: 3px solid var(--rose);
  border-radius: 0 12px 12px 0; padding: 1rem 1.2rem; margin: 1rem 0;
}
.activity-box strong { color: var(--rose); }
.activity-box p, .activity-box li { font-size: 0.88rem; }
.activity-box ul { padding-left: 1.2rem; margin-top: 0.5rem; }
.tip-box {
  background: rgba(251,191,36,0.06); border-left: 3px solid var(--amber);
  border-radius: 0 12px 12px 0; padding: 1rem 1.2rem; margin: 1rem 0;
}
.tip-box strong { color: var(--amber); }
.tip-box p { font-size: 0.88rem; }

/* Complete button */
.complete-btn {
  display: inline-flex; align-items: center; gap: 0.5rem;
  margin-top: 1.2rem; padding: 0.6rem 1.2rem; border-radius: 100px;
  border: 1px solid var(--border); background: transparent; color: var(--text-sec);
  font-family: var(--font); font-size: 0.82rem; font-weight: 600; cursor: pointer; transition: all 0.3s;
}
.complete-btn:hover { background: rgba(45,212,191,0.1); border-color: rgba(45,212,191,0.3); color: var(--teal); }
.complete-btn.done { background: rgba(45,212,191,0.12); border-color: rgba(45,212,191,0.3); color: var(--teal); }

/* Quiz */
.quiz-section {
  background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 2rem; margin-top: 2rem; animation: fadeInUp 1.8s ease;
}
.quiz-section h3 { font-family: var(--font-d); font-size: 1.15rem; font-weight: 700; margin-bottom: 1rem; }
.quiz-q { font-size: 0.95rem; font-weight: 600; margin-bottom: 1rem; }
.quiz-options { list-style: none; }
.quiz-opt {
  padding: 0.7rem 1rem; margin-bottom: 0.5rem;
  border: 1px solid var(--border); border-radius: 12px;
  cursor: pointer; font-size: 0.9rem; color: var(--text-sec); transition: all 0.3s;
}
.quiz-opt:hover { background: var(--bg-card-hover); border-color: rgba(255,255,255,0.12); }
.quiz-opt.correct { background: rgba(45,212,191,0.1); border-color: rgba(45,212,191,0.3); color: var(--teal); }
.quiz-opt.wrong { background: rgba(251,113,133,0.08); border-color: rgba(251,113,133,0.3); color: var(--rose); }
.quiz-feedback { margin-top: 0.8rem; font-size: 0.88rem; padding: 0.8rem 1rem; border-radius: 12px; display: none; }
.quiz-feedback.show { display: block; }
.quiz-feedback.success { background: rgba(45,212,191,0.08); color: var(--teal); }
.quiz-feedback.error { background: rgba(251,113,133,0.06); color: var(--rose); }

/* Navigation */
.mod-nav { display: flex; justify-content: space-between; align-items: center; padding: 2.5rem 0 1.5rem; gap: 1rem; }
.nav-btn {
  display: inline-flex; align-items: center; gap: 0.5rem;
  padding: 0.8rem 1.5rem; border-radius: 100px;
  text-decoration: none; font-size: 0.88rem; font-weight: 600; transition: all 0.3s;
}
.nav-prev { color: var(--text-sec); border: 1px solid var(--border); }
.nav-prev:hover { border-color: rgba(255,255,255,0.15); color: var(--text); }
.nav-next {
  background: linear-gradient(135deg, var(--accent), var(--accent2)); color: #fff; border: none;
}
.nav-next:hover { opacity: 0.9; transform: translateY(-2px); box-shadow: 0 8px 25px rgba(79,140,255,0.3); }

footer { text-align: center; padding: 2rem 0; color: var(--text-muted); font-size: 0.78rem; }

@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
@keyframes fadeInDown { from { opacity: 0; transform: translateY(-20px); } to { opacity: 1; transform: translateY(0); } }
@keyframes fadeInUp { from { opacity: 0; transform: translateY(25px); } to { opacity: 1; transform: translateY(0); } }

@media (max-width: 640px) {
  .container { padding: 1rem; }
  .lesson-header { padding: 1rem 1.2rem; }
  .lesson-content { padding: 0 1.2rem 1.2rem; }
  .mod-nav { flex-direction: column; }
  .nav-btn { width: 100%; justify-content: center; }
  .objectives { padding: 1.2rem 1.4rem; }
}