:root {
  --bg: #f4f6fb;
  --card: #ffffff;
  --text: #1f2937;
  --muted: #6b7280;
  --shadow: 0 10px 30px rgba(15, 23, 42, 0.08);
  --radius: 18px;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  color: var(--text);
  background:
    radial-gradient(circle at top left, rgba(99, 102, 241, 0.12), transparent 28%),
    radial-gradient(circle at top right, rgba(16, 185, 129, 0.12), transparent 24%),
    var(--bg);
}

.home {
  max-width: 1080px;
  margin: 0 auto;
  padding: 48px 20px 64px;
}

.hero {
  text-align: center;
  margin-bottom: 40px;
}

.eyebrow {
  margin: 0 0 10px;
  letter-spacing: 0.24em;
  font-size: 12px;
  color: var(--muted);
}

.hero h1 {
  margin: 0;
  font-size: clamp(2rem, 5vw, 3rem);
}

.subtitle {
  margin: 12px auto 0;
  max-width: 560px;
  color: var(--muted);
  line-height: 1.7;
}

.auth-card {
  max-width: 480px;
  margin: 0 auto 32px;
  padding: 24px;
  border-radius: var(--radius);
  background: var(--card);
  box-shadow: var(--shadow);
  border: 1px solid rgba(148, 163, 184, 0.18);
}

.auth-card h2 {
  margin: 0 0 8px;
  font-size: 1.2rem;
}

.auth-hint {
  margin: 0 0 16px;
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.6;
}

.auth-row {
  display: flex;
  gap: 10px;
}

.auth-row input {
  flex: 1;
  min-width: 0;
  padding: 10px 12px;
  border: 1px solid rgba(148, 163, 184, 0.35);
  border-radius: 10px;
  font-size: 1rem;
}

.auth-row button,
.auth-logout {
  padding: 10px 16px;
  border: none;
  border-radius: 10px;
  background: #2563eb;
  color: #fff;
  font-weight: 600;
  cursor: pointer;
}

.auth-logout {
  margin-top: 12px;
  background: #fff;
  color: var(--text);
  border: 1px solid rgba(148, 163, 184, 0.35);
}

.auth-error {
  margin: 12px 0 0;
  color: #dc2626;
  font-size: 0.9rem;
}

.auth-welcome {
  margin: 12px 0 0;
  color: #15803d;
  font-size: 0.92rem;
}

.subjects {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 18px;
}

.subject-card {
  display: block;
  padding: 28px 24px;
  border-radius: var(--radius);
  background: var(--card);
  box-shadow: var(--shadow);
  text-decoration: none;
  color: inherit;
  transition: transform 0.18s ease, box-shadow 0.18s ease;
  border: 1px solid rgba(148, 163, 184, 0.18);
}

.subject-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 16px 36px rgba(15, 23, 42, 0.12);
}

.subject-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 48px;
  height: 48px;
  border-radius: 14px;
  font-weight: 700;
  margin-bottom: 16px;
}

.chinese .subject-icon { background: #fee2e2; color: #b91c1c; }
.english .subject-icon { background: #dbeafe; color: #1d4ed8; }
.math .subject-icon { background: #ede9fe; color: #6d28d9; }
.physics .subject-icon { background: #dcfce7; color: #15803d; }

.subject-card h2 {
  margin: 0 0 8px;
  font-size: 1.35rem;
}

.subject-card p {
  margin: 0;
  color: var(--muted);
  line-height: 1.6;
  font-size: 0.95rem;
}

.footer {
  margin-top: 40px;
  text-align: center;
  color: var(--muted);
  font-size: 0.92rem;
}

.footer code {
  background: rgba(148, 163, 184, 0.16);
  padding: 2px 6px;
  border-radius: 6px;
}

@media (max-width: 640px) {
  .home {
    padding-top: 28px;
  }
}