:root {
  --bg: #F4EFE6;
  --surface: #FFFFFF;
  --fg: #18181B;
  --fg-muted: #71717A;
  --accent: #1E3A5F;
  --accent-light: #E8F0F9;
  --highlight: #D97706;
  --highlight-light: #FEF3C7;
  --bio-color: #059669;
  --chem-color: #7C3AED;
  --eng-color: #DC2626;
  --border: #E5E2DC;
  --code-bg: #1E1E2E;
}

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

body {
  background: var(--bg);
  color: var(--fg);
  font-family: 'DM Sans', sans-serif;
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

/* Navigation */
.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 48px;
}

.nav-brand {
  font-family: 'Syne', sans-serif;
  font-weight: 800;
  font-size: 20px;
  color: var(--accent);
  letter-spacing: -0.5px;
}

.nav-tag {
  font-size: 12px;
  font-weight: 500;
  color: var(--fg-muted);
  background: var(--accent-light);
  padding: 4px 10px;
  border-radius: 20px;
  letter-spacing: 0.5px;
}

.nav-cta {
  font-size: 13px;
  font-weight: 700;
  color: white;
  background: var(--bio-color);
  padding: 6px 14px;
  border-radius: 20px;
  text-decoration: none;
  transition: background 0.15s;
  white-space: nowrap;
}
.nav-cta:hover { background: #047857; }

/* Hero */
.hero {
  padding: 0 48px 80px;
}

.hero-inner {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 60px;
  align-items: center;
  max-width: 1200px;
  margin: 0 auto;
}

.hero-badge {
  display: inline-block;
  background: var(--highlight);
  color: white;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 1px;
  text-transform: uppercase;
  padding: 4px 10px;
  border-radius: 3px;
  margin-bottom: 20px;
}

.hero-headline {
  font-family: 'Syne', sans-serif;
  font-size: 44px;
  font-weight: 800;
  line-height: 1.1;
  color: var(--accent);
  margin-bottom: 24px;
  letter-spacing: -1px;
}

.hero-lede {
  font-size: 17px;
  color: var(--fg-muted);
  line-height: 1.65;
  margin-bottom: 36px;
  max-width: 480px;
}

.hero-meta {
  display: flex;
  align-items: center;
  gap: 20px;
}

.hero-stat {
  font-size: 13px;
  color: var(--fg-muted);
}

.hero-stat strong {
  color: var(--fg);
  font-weight: 600;
}

.hero-sep {
  width: 1px;
  height: 16px;
  background: var(--border);
}

/* Phone mockup */
.hero-visual {
  display: flex;
  justify-content: center;
}

.phone-frame {
  width: 260px;
  background: #1A1A2E;
  border-radius: 36px;
  padding: 12px;
  box-shadow: 0 30px 60px rgba(0,0,0,0.18), 0 0 0 1px rgba(255,255,255,0.08);
}

.phone-screen {
  background: #FAFAF9;
  border-radius: 28px;
  padding: 20px 16px;
  min-height: 420px;
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.screen-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.screen-title {
  font-family: 'Syne', sans-serif;
  font-size: 13px;
  font-weight: 700;
  color: var(--accent);
}

.screen-progress {
  font-size: 12px;
  font-weight: 600;
  color: var(--bio-color);
}

.screen-question {
  background: white;
  border-radius: 14px;
  padding: 14px;
  border: 1.5px solid var(--border);
}

.q-text {
  font-size: 12px;
  color: var(--fg);
  line-height: 1.5;
  margin-bottom: 12px;
  font-weight: 500;
}

.q-options {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.q-opt {
  font-size: 11px;
  padding: 7px 10px;
  border-radius: 8px;
  border: 1.5px solid var(--border);
  color: var(--fg-muted);
  font-weight: 500;
}

.q-opt.selected {
  border-color: var(--accent);
  background: var(--accent-light);
  color: var(--accent);
}

.q-opt.correct {
  border-color: var(--bio-color);
  background: #D1FAE5;
  color: #065F46;
}

.correct-feedback {
  font-size: 11px;
  background: #D1FAE5;
  color: #065F46;
  padding: 8px 12px;
  border-radius: 8px;
  font-weight: 500;
}

.feedback-icon {
  margin-right: 5px;
  font-weight: 700;
}

.screen-progress-bar {
  height: 4px;
  background: var(--border);
  border-radius: 2px;
  overflow: hidden;
  margin-top: auto;
}

.progress-fill {
  height: 100%;
  background: var(--bio-color);
  border-radius: 2px;
  transition: width 0.3s;
}

/* Subjects */
.subjects {
  background: white;
  padding: 80px 48px;
}

.subjects-inner {
  max-width: 1200px;
  margin: 0 auto;
}

.section-label {
  font-family: 'Syne', sans-serif;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: var(--fg-muted);
  margin-bottom: 40px;
}

.subject-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 28px;
}

.subject-card {
  background: var(--bg);
  border-radius: 20px;
  padding: 32px 28px;
  border: 1.5px solid var(--border);
  transition: transform 0.2s, box-shadow 0.2s;
}

.subject-card:hover {
  transform: translateY(-3px);
  box-shadow: 0 12px 30px rgba(0,0,0,0.06);
}

.subject-icon {
  width: 44px;
  height: 44px;
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 18px;
}

.subject-icon svg {
  width: 24px;
  height: 24px;
}

.bio-icon {
  background: #D1FAE5;
  color: var(--bio-color);
}

.chem-icon {
  background: #EDE9FE;
  color: var(--chem-color);
}

.eng-icon {
  background: #FEE2E2;
  color: var(--eng-color);
}

.subject-card h3 {
  font-family: 'Syne', sans-serif;
  font-size: 20px;
  font-weight: 700;
  color: var(--fg);
  margin-bottom: 10px;
}

.subject-card p {
  font-size: 14px;
  color: var(--fg-muted);
  line-height: 1.6;
  margin-bottom: 18px;
}

.subject-tag {
  font-size: 11px;
  font-weight: 600;
  color: var(--fg-muted);
  background: var(--surface);
  border: 1px solid var(--border);
  padding: 3px 8px;
  border-radius: 6px;
}

/* Features */
.features {
  padding: 100px 48px;
}

.features-inner {
  max-width: 1200px;
  margin: 0 auto;
}

.features-header {
  max-width: 560px;
  margin-bottom: 60px;
}

.features-header h2 {
  font-family: 'Syne', sans-serif;
  font-size: 36px;
  font-weight: 800;
  color: var(--accent);
  line-height: 1.15;
  margin-bottom: 16px;
  letter-spacing: -0.5px;
}

.features-header p {
  font-size: 17px;
  color: var(--fg-muted);
  line-height: 1.6;
}

.feature-list {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0;
  border-top: 1.5px solid var(--border);
}

.feature-item {
  display: flex;
  gap: 24px;
  padding: 36px 0;
  border-bottom: 1.5px solid var(--border);
}

.feature-item:nth-child(odd) {
  padding-right: 48px;
  border-right: 1.5px solid var(--border);
}

.feature-item:nth-child(even) {
  padding-left: 48px;
}

.feature-num {
  font-family: 'Syne', sans-serif;
  font-size: 11px;
  font-weight: 800;
  color: var(--highlight);
  letter-spacing: 1px;
  flex-shrink: 0;
  padding-top: 3px;
}

.feature-content h3 {
  font-family: 'Syne', sans-serif;
  font-size: 17px;
  font-weight: 700;
  color: var(--fg);
  margin-bottom: 8px;
}

.feature-content p {
  font-size: 14px;
  color: var(--fg-muted);
  line-height: 1.65;
}

/* Demo */
.demo {
  background: var(--accent);
  padding: 80px 48px;
}

.demo-inner {
  max-width: 760px;
  margin: 0 auto;
}

.demo-label {
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: rgba(255,255,255,0.4);
  margin-bottom: 24px;
}

.demo-card {
  background: rgba(255,255,255,0.07);
  border: 1px solid rgba(255,255,255,0.12);
  border-radius: 20px;
  padding: 32px;
  margin-bottom: 20px;
}

.demo-meta {
  font-size: 11px;
  color: rgba(255,255,255,0.4);
  font-weight: 600;
  letter-spacing: 0.5px;
  margin-bottom: 16px;
}

.demo-q {
  font-size: 17px;
  color: white;
  line-height: 1.6;
  margin-bottom: 20px;
  font-weight: 500;
}

.demo-options {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
}

.demo-opt {
  font-size: 13px;
  color: rgba(255,255,255,0.6);
  background: rgba(255,255,255,0.06);
  padding: 10px 14px;
  border-radius: 10px;
  border: 1px solid rgba(255,255,255,0.1);
}

.demo-answer {
  padding: 14px 18px;
  background: rgba(255,255,255,0.1);
  border-radius: 10px;
  margin-bottom: 16px;
}

.answer-label {
  font-size: 12px;
  color: rgba(255,255,255,0.5);
  margin-right: 8px;
  font-weight: 600;
}

.demo-answer span:last-child {
  font-family: 'Syne', sans-serif;
  font-weight: 700;
  color: white;
  font-size: 16px;
}

.demo-explanation {
  background: rgba(255,255,255,0.05);
  border-radius: 12px;
  padding: 20px;
}

.demo-explanation p {
  font-size: 14px;
  color: rgba(255,255,255,0.7);
  line-height: 1.7;
}

/* Closing */
.closing {
  background: #18181B;
  padding: 100px 48px;
}

.closing-inner {
  max-width: 720px;
  margin: 0 auto;
  text-align: center;
}

.closing h2 {
  font-family: 'Syne', sans-serif;
  font-size: 36px;
  font-weight: 800;
  color: white;
  line-height: 1.2;
  margin-bottom: 24px;
  letter-spacing: -0.5px;
}

.closing p {
  font-size: 17px;
  color: rgba(255,255,255,0.5);
  line-height: 1.7;
  margin-bottom: 16px;
}

/* Footer */
.footer {
  background: #111;
  padding: 48px;
}

.footer-inner {
  max-width: 1200px;
  margin: 0 auto;
}

.footer-brand {
  font-family: 'Syne', sans-serif;
  font-weight: 800;
  font-size: 18px;
  color: white;
  margin-bottom: 8px;
}

.footer-tagline {
  font-size: 14px;
  color: rgba(255,255,255,0.4);
  margin-bottom: 6px;
}

.footer-subjects {
  font-size: 12px;
  color: rgba(255,255,255,0.25);
  letter-spacing: 1px;
}

/* Responsive */
@media (max-width: 900px) {
  .hero-inner { grid-template-columns: 1fr; }
  .hero-visual { display: none; }
  .hero-headline { font-size: 32px; }
  .subject-grid { grid-template-columns: 1fr; }
  .feature-list { grid-template-columns: 1fr; }
  .feature-item:nth-child(odd) { border-right: none; padding-right: 0; }
  .feature-item:nth-child(even) { padding-left: 0; }
  .demo-options { grid-template-columns: 1fr; }
  .nav, .hero, .subjects, .features, .demo, .closing, .footer { padding-left: 24px; padding-right: 24px; }
}