* { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --bg: #f5f7fa;
  --panel: #ffffff;
  --ink: #1f2933;
  --muted: #6b7785;
  --brand: #2f6df0;
  --brand-soft: #e8f0fe;
  --line: #e3e8ef;
  --accent: #ff7043;
}
html, body { height: 100%; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  background: var(--bg);
  color: var(--ink);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Header */
.home-header {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 18px 24px;
  background: var(--panel);
  border-bottom: 1px solid var(--line);
  position: sticky;
  top: 0;
  z-index: 20;
}
.home-header .brand { display: flex; align-items: center; gap: 12px; }
.home-header .logo { font-size: 30px; }
.home-header h1 { font-size: 19px; font-weight: 700; }
.home-header .sub { font-size: 13px; color: var(--muted); margin-top: 2px; }
.back-home {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 38px; height: 38px;
  border-radius: 50%;
  border: 1px solid var(--line);
  background: var(--panel);
  color: var(--ink);
  text-decoration: none;
  font-size: 22px;
  line-height: 1;
  flex-shrink: 0;
}
.back-home:hover { border-color: var(--brand); color: var(--brand); }
.home-header .topbar-right { margin-left: auto; }

/* Main */
.home-main {
  flex: 1;
  width: 100%;
  max-width: 960px;
  margin: 0 auto;
  padding: 32px 20px 48px;
}
.section-title { font-size: 16px; color: var(--muted); font-weight: 600; margin-bottom: 18px; }

/* Grid of cards */
.grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 18px;
}
.card {
  display: flex;
  flex-direction: column;
  gap: 6px;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 22px 20px;
  text-decoration: none;
  color: inherit;
  cursor: pointer;
  transition: transform .12s, box-shadow .15s, border-color .15s;
  position: relative;
  min-height: 120px;
}
.card:hover {
  transform: translateY(-3px);
  box-shadow: 0 8px 24px rgba(31,41,51,.08);
  border-color: transparent;
}
.card-icon { font-size: 34px; }
.card-title { font-size: 18px; font-weight: 700; margin-top: 4px; }
.card-desc { font-size: 13px; color: var(--muted); line-height: 1.5; }
.card-go {
  margin-top: auto;
  font-size: 13px;
  font-weight: 600;
  color: var(--brand);
}
.card-disabled {
  cursor: default;
  opacity: .85;
}
.card-disabled:hover { transform: none; box-shadow: none; border-color: var(--line); }
.card-disabled .card-go { color: var(--muted); }

/* 分类主题色 */
.card-en   { border-top: 4px solid #2f6df0; }
.card-math { border-top: 4px solid #16a34a; }
.card-cn   { border-top: 4px solid #e0457b; }
.card-rec  { border-top: 4px solid #f5a524; }

/* Footer */
.home-footer {
  text-align: center;
  font-size: 12px;
  color: var(--muted);
  padding: 20px;
  border-top: 1px solid var(--line);
}

/* Responsive */
@media (max-width: 600px) {
  .grid { grid-template-columns: 1fr; }
  .home-header { padding: 14px 16px; }
  .home-main { padding: 22px 16px 36px; }
}