:root {
  --blue: #2468d8;
  --text: #162033;
  --muted: #69758a;
  --line: #dfe5ef;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  min-height: 100vh;
  color: var(--text);
  background: #eef3fb;
  font-family: "Microsoft YaHei", "PingFang SC", Arial, sans-serif;
}
button, input { font: inherit; }
a { color: var(--blue); text-decoration: none; }
.course-shell { min-height: 100vh; }
.login-view { display: grid; place-items: center; min-height: 100vh; padding: 24px; }
.login-card {
  width: min(420px, 100%);
  padding: 26px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  box-shadow: 0 14px 34px rgba(31, 46, 76, .12);
}
.brand { display: inline-flex; padding: 6px 10px; border-radius: 999px; color: #fff; background: var(--blue); font-weight: 800; }
h1 { margin: 16px 0 8px; font-size: 26px; }
p { color: var(--muted); line-height: 1.7; }
label { display: grid; gap: 6px; margin-top: 12px; color: var(--muted); font-size: 13px; }
input { min-height: 40px; padding: 8px 10px; border: 1px solid var(--line); border-radius: 8px; }
button { min-height: 40px; padding: 0 16px; border: 0; border-radius: 8px; color: #fff; background: var(--blue); cursor: pointer; }
.login-card button { width: 100%; margin: 16px 0 12px; }
.error { min-height: 20px; color: #b42318; font-size: 13px; }
.topbar { display: flex; justify-content: space-between; align-items: center; padding: 18px 28px; background: #fff; border-bottom: 1px solid var(--line); }
.topbar strong { display: block; font-size: 18px; }
.topbar span { display: block; margin-top: 3px; color: var(--muted); font-size: 13px; }
.hero { min-height: 380px; display: grid; align-items: center; padding: 48px; background: linear-gradient(120deg, rgba(36,104,216,.88), rgba(20,136,95,.76)), url("../腾讯-人工智能通识课平台/frontend/public/images/optimized/11-lg.webp") center / cover; color: #fff; }
.hero h1 { max-width: 760px; font-size: 42px; }
.hero p { max-width: 680px; color: rgba(255,255,255,.88); }
.hero button { margin-top: 12px; color: var(--blue); background: #fff; }
.cards { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 16px; padding: 24px; }
.cards article { padding: 20px; border: 1px solid var(--line); border-radius: 8px; background: #fff; }
.cards strong, .cards span { display: block; }
.cards span { margin-top: 8px; color: var(--blue); font-size: 24px; font-weight: 800; }
@media (max-width: 820px) {
  .cards { grid-template-columns: 1fr; }
  .hero { padding: 28px; }
  .hero h1 { font-size: 32px; }
}