:root {
  --bg: #f6f8fc;
  --panel: #ffffff;
  --ink: #142033;
  --muted: #657188;
  --line: #dfe6f1;
  --blue: #2563eb;
  --blue-2: #19a7ce;
  --green: #16a34a;
  --shadow: 0 18px 48px rgba(29, 52, 87, .12);
}
* { box-sizing: border-box; }
body { margin: 0; font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif; color: var(--ink); background: radial-gradient(circle at top left, #e9f3ff 0, transparent 32rem), var(--bg); }
a { color: inherit; text-decoration: none; }
button, input { font: inherit; }
.topbar { min-height: 72px; padding: 0 32px; display: flex; align-items: center; justify-content: space-between; border-bottom: 1px solid rgba(223,230,241,.8); background: rgba(255,255,255,.78); backdrop-filter: blur(18px); position: sticky; top: 0; z-index: 10; }
.brand { display: inline-flex; align-items: center; gap: 10px; font-weight: 800; }
.brand-mark, .avatar { width: 38px; height: 38px; display: inline-grid; place-items: center; border-radius: 10px; color: #fff; font-weight: 900; background: linear-gradient(135deg, var(--blue), var(--blue-2)); box-shadow: 0 10px 24px rgba(37, 99, 235, .25); }
.nav { display: flex; align-items: center; gap: 14px; color: var(--muted); }
.nav form { margin: 0; }
.nav a.active { color: var(--blue); font-weight: 700; }
.page { width: min(1120px, calc(100% - 32px)); margin: 0 auto; padding: 38px 0 64px; }
.hero, .dashboard { display: grid; grid-template-columns: 1.05fr .95fr; gap: 26px; align-items: center; }
.hero { min-height: calc(100vh - 130px); }
.eyebrow { margin: 0 0 12px; color: var(--blue); font-size: 13px; font-weight: 800; letter-spacing: 0; text-transform: uppercase; }
h1 { margin: 0; font-size: clamp(34px, 6vw, 66px); line-height: .98; letter-spacing: 0; }
h2 { margin: 0 0 14px; font-size: 22px; }
.lead { max-width: 630px; margin: 22px 0; color: var(--muted); font-size: 20px; line-height: 1.55; }
.hero-actions { display: flex; align-items: center; gap: 18px; flex-wrap: wrap; }
.button { border: 0; cursor: pointer; display: inline-flex; align-items: center; justify-content: center; min-height: 48px; padding: 0 22px; border-radius: 8px; color: #fff; font-weight: 800; background: linear-gradient(135deg, var(--blue), var(--blue-2)); box-shadow: 0 14px 32px rgba(37, 99, 235, .28); }
.button.small { min-height: 38px; padding: 0 14px; }
.button.wide { width: 100%; margin-top: 18px; }
.ghost { border: 1px solid var(--line); background: #fff; border-radius: 8px; min-height: 38px; padding: 0 14px; cursor: pointer; color: var(--muted); }
.text-link { color: var(--blue); font-weight: 800; }
.mentor-panel, .card, .plan-card, .auth-card, .lesson-card { background: rgba(255,255,255,.92); border: 1px solid rgba(223,230,241,.86); border-radius: 8px; box-shadow: var(--shadow); }
.mentor-panel { padding: 26px; }
.preview-panel { transform: rotate(1deg); }
.mentor-head { display: flex; gap: 14px; align-items: center; margin-bottom: 22px; }
.mentor-head b { display: block; font-size: 20px; }
.mentor-head span { display: block; color: var(--muted); margin-top: 4px; line-height: 1.45; }
.score-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; margin: 18px 0; }
.score-grid div { min-height: 96px; border-radius: 8px; padding: 16px; background: #f2f6ff; border: 1px solid #dbe7ff; }
.score-grid span { display: block; color: var(--muted); font-size: 13px; font-weight: 700; }
.score-grid b { display: block; margin-top: 8px; font-size: 34px; }
.score-grid.compact div { min-height: 82px; }
.admin-stats { max-width: 760px; }
.topic-row { display: grid; grid-template-columns: 120px 1fr; gap: 14px; align-items: center; margin-top: 14px; color: var(--muted); font-weight: 700; }
.progress { height: 10px; border-radius: 999px; background: #e8edf6; overflow: hidden; }
.progress span { display: block; height: 100%; border-radius: inherit; background: linear-gradient(90deg, var(--blue), var(--green)); }
.section-head { margin-bottom: 24px; }
.section-head h1 { font-size: clamp(30px, 5vw, 52px); max-width: 820px; }
.cards, .topic-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; }
.card, .plan-card, .auth-card, .lesson-card { padding: 22px; }
.card p, .plan-card p, .auth-card p { color: var(--muted); line-height: 1.55; }
.card-title { display: flex; justify-content: space-between; gap: 16px; align-items: baseline; }
.card-title span { color: var(--blue); font-weight: 900; }
.plan-card { align-self: stretch; }
.lesson-link { display: flex; justify-content: space-between; gap: 14px; align-items: center; padding: 14px 0; border-bottom: 1px solid var(--line); }
.lesson-link:last-child { border-bottom: 0; }
.lesson-link b { color: var(--blue); }
.auth-card { max-width: 460px; margin: 8vh auto; }
.auth-card h1 { font-size: 38px; }
.form { display: grid; gap: 14px; margin-top: 20px; }
.form label { display: grid; gap: 8px; color: var(--muted); font-weight: 700; }
.form input { min-height: 48px; border-radius: 8px; border: 1px solid var(--line); padding: 0 14px; background: #fff; color: var(--ink); }
.demo-logins { margin-top: 18px; padding: 14px; border-radius: 8px; background: #f2f6ff; color: var(--muted); line-height: 1.6; }
.notice { margin: 18px 0; padding: 14px 16px; border-radius: 8px; background: #ecfdf5; border: 1px solid #bbf7d0; color: #166534; font-weight: 700; }
.notice.error { background: #fff1f2; border-color: #fecdd3; color: #be123c; }
.lesson-shell { display: grid; place-items: center; min-height: calc(100vh - 170px); }
.lesson-card { width: min(760px, 100%); }
.lesson-card h1 { font-size: clamp(28px, 5vw, 46px); line-height: 1.1; }
.answer-form { grid-template-columns: 1fr auto; align-items: end; }
.explain { margin: 16px 0 20px; padding: 18px; border-radius: 8px; background: #f8fbff; border: 1px solid var(--line); }
.install-card { text-align: left; }
@media (max-width: 860px) { .topbar { padding: 0 16px; } .page { width: min(100% - 24px, 1120px); padding-top: 24px; } .hero, .dashboard { grid-template-columns: 1fr; } .hero { min-height: auto; } h1 { font-size: 42px; } .cards, .topic-grid { grid-template-columns: 1fr; } .score-grid { grid-template-columns: 1fr; } .answer-form { grid-template-columns: 1fr; } .preview-panel { transform: none; } }
@media (max-width: 520px) { .brand span:last-child { display: none; } .nav { gap: 8px; } h1 { font-size: 34px; } .lead { font-size: 17px; } .mentor-panel, .card, .plan-card, .auth-card, .lesson-card { padding: 18px; } .topic-row { grid-template-columns: 1fr; gap: 8px; } }