:root {
  color-scheme: light;
  --color-primary: #1a3a5c;
  --color-primary-hover: #2e6bc6;
  --color-background: #f5f7fa;
  --color-surface: #ffffff;
  --color-text: #1a1a2e;
  --color-muted-text: #5a6474;
  --color-border: #d8dee6;
  --color-focus: #2e6bc6;
  --font-body: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", ui-sans-serif, system-ui, sans-serif;
  --font-display: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", ui-sans-serif, system-ui, sans-serif;
  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --space-unit: 0.25rem;
  --content-width: 72rem;
}

* {
  box-sizing: border-box;
}

html {
  background: var(--color-background);
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: 18px;
  line-height: 1.6;
}

body {
  margin: 0;
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
}

button,
input,
select,
textarea {
  font: inherit;
}

:focus-visible {
  outline: 3px solid var(--color-focus);
  outline-offset: 3px;
}

.skip-link {
  left: 1rem;
  position: fixed;
  top: 1rem;
  transform: translateY(-200%);
  z-index: 100;
  background: var(--color-surface);
  padding: 0.5rem 1rem;
  border-radius: var(--radius-sm);
  text-decoration: none;
  color: var(--color-primary);
  font-weight: 600;
}

.skip-link:focus {
  transform: translateY(0);
}

/* ===== Header ===== */
.site-header {
  background: var(--color-primary);
  color: #ffffff;
  padding: 1rem 2rem;
  display: flex;
  align-items: center;
  gap: 1.5rem;
}

.site-header .app-name {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-decoration: none;
  color: #ffffff;
}

.site-header .back-link {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  color: rgba(255, 255, 255, 0.85);
  text-decoration: none;
  font-size: 0.95rem;
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-sm);
  border: 1px solid rgba(255, 255, 255, 0.3);
  transition: background 0.15s, color 0.15s;
}

.site-header .back-link:hover {
  background: rgba(255, 255, 255, 0.1);
  color: #ffffff;
}

/* ===== Main ===== */
main {
  flex: 1;
  max-width: var(--content-width);
  width: 100%;
  margin: 0 auto;
  padding: 3rem 2rem;
}

/* ===== Homepage ===== */
.home-hero {
  text-align: center;
  margin-bottom: 3rem;
}

.home-hero h1 {
  font-size: 2.2rem;
  font-weight: 700;
  color: var(--color-primary);
  margin: 0 0 0.5rem;
  letter-spacing: 0.04em;
}

.home-hero p {
  font-size: 1.1rem;
  color: var(--color-muted-text);
  margin: 0;
}

.card-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1.5rem;
}

.feature-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 2.5rem 2rem;
  text-decoration: none;
  color: var(--color-text);
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: 1rem;
  transition: box-shadow 0.2s, transform 0.2s;
}

.feature-card:hover {
  box-shadow: 0 8px 24px rgba(26, 58, 92, 0.12);
  transform: translateY(-3px);
}

.feature-card .card-icon {
  width: 4rem;
  height: 4rem;
  background: var(--color-background);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.8rem;
  color: var(--color-primary);
}

.feature-card .card-title {
  font-size: 1.35rem;
  font-weight: 600;
  color: var(--color-primary);
}

.feature-card .card-desc {
  font-size: 0.95rem;
  color: var(--color-muted-text);
  line-height: 1.5;
}

/* ===== Sub Pages ===== */
.sub-page-header {
  margin-bottom: 2.5rem;
}

.sub-page-header h1 {
  font-size: 1.8rem;
  font-weight: 700;
  color: var(--color-primary);
  margin: 0 0 0.5rem;
}

.sub-page-header p {
  font-size: 1rem;
  color: var(--color-muted-text);
  margin: 0;
}

.placeholder-content {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 3rem 2rem;
  text-align: center;
}

.placeholder-content .placeholder-icon {
  font-size: 3rem;
  margin-bottom: 1rem;
  opacity: 0.6;
}

.placeholder-content h2 {
  font-size: 1.3rem;
  color: var(--color-primary);
  margin: 0 0 0.75rem;
}

.placeholder-content p {
  font-size: 1rem;
  color: var(--color-muted-text);
  margin: 0;
  max-width: 32rem;
  margin-left: auto;
  margin-right: auto;
}

/* ===== Footer ===== */
.site-footer {
  text-align: center;
  padding: 1.5rem 2rem;
  color: var(--color-muted-text);
  font-size: 0.85rem;
  border-top: 1px solid var(--color-border);
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
  }
}