/* ============================================
   eznju — 南京大学学生开发者生态
   主题变量集中管理，方便后续换肤
   ============================================ */

:root {
  --color-bg: #f8f7fa;
  --color-surface: #ffffff;
  --color-surface-alt: #f3f1f5;
  --color-border: #e4e0eb;
  --color-text: #1f2328;
  --color-text-muted: #656d76;
  --color-primary: #6b2d8b;
  --color-primary-hover: #552372;
  --color-primary-text: #ffffff;
  --color-tag-bg: #f0e8f5;
  --color-tag-text: #6b2d8b;

  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 16px;

  --shadow-card: 0 1px 3px rgba(0, 0, 0, 0.04), 0 1px 2px rgba(0, 0, 0, 0.03);
  --shadow-card-hover: 0 4px 14px rgba(107, 45, 139, 0.08);

  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans SC",
    "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-mono: "SF Mono", "Fira Code", "Fira Mono", "Roboto Mono", monospace;

  --container-max: 1080px;
}

/* Reset */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  font-size: 15px;
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-bg);
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--color-primary);
  text-decoration: none;
}

a:hover {
  color: var(--color-primary-hover);
}

.container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 24px;
}

/* ============================================
   Hero
   ============================================ */

.hero {
  padding: 40px 0 32px;
  text-align: center;
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  position: relative;
  overflow: hidden;
}

.hero-logo {
  font-family: var(--font-mono);
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--color-text);
  margin-bottom: 6px;
  display: inline-block;
}

.hero-logo .logo-bracket {
  color: var(--color-primary);
  font-weight: 400;
  opacity: 0.7;
}

.hero-title {
  font-size: 1rem;
  font-weight: 500;
  color: var(--color-text-muted);
  margin-bottom: 4px;
}

.hero-tagline {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  opacity: 0.75;
}

.hero-decoration {
  position: absolute;
  font-family: var(--font-mono);
  font-size: 6rem;
  font-weight: 700;
  color: var(--color-primary);
  opacity: 0.03;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  pointer-events: none;
  user-select: none;
}

/* ============================================
   Sections
   ============================================ */

.section {
  padding: 32px 0;
}

.section-alt {
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  border-bottom: 1px solid var(--color-border);
}

.section-title {
  font-size: 1.15rem;
  font-weight: 600;
  text-align: center;
  margin-bottom: 4px;
}

.section-desc {
  text-align: center;
  color: var(--color-text-muted);
  margin-bottom: 20px;
  font-size: 0.88rem;
}

/* ============================================
   Cards
   ============================================ */

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 16px;
}

.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 18px;
  transition: box-shadow 0.2s ease, transform 0.2s ease;
  display: flex;
  flex-direction: column;
}

.section-alt .card {
  background: var(--color-bg);
}

.card:hover {
  box-shadow: var(--shadow-card-hover);
  transform: translateY(-1px);
}

.card-title {
  font-size: 1.05rem;
  font-weight: 600;
  margin-bottom: 8px;
}

.card-title-en {
  font-weight: 400;
  color: var(--color-text-muted);
  font-size: 0.85rem;
  margin-left: 4px;
}

.card-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
  margin-bottom: 10px;
}

.tag {
  font-size: 0.72rem;
  padding: 2px 8px;
  background: var(--color-tag-bg);
  color: var(--color-tag-text);
  border-radius: var(--radius-sm);
  font-weight: 500;
}

.card-desc {
  color: var(--color-text-muted);
  font-size: 0.88rem;
  margin-bottom: 12px;
  flex: 1;
}

.card-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

/* ============================================
   Buttons
   ============================================ */

.btn {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 6px 14px;
  border-radius: var(--radius-sm);
  font-size: 0.82rem;
  font-weight: 500;
  border: 1px solid transparent;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease, border-color 0.15s ease;
  white-space: nowrap;
}

.btn-primary {
  background: var(--color-primary);
  color: var(--color-primary-text);
  border-color: var(--color-primary);
}

.btn-primary:hover {
  background: var(--color-primary-hover);
  border-color: var(--color-primary-hover);
  color: var(--color-primary-text);
}

.btn-outline {
  background: transparent;
  color: var(--color-text);
  border-color: var(--color-border);
}

.btn-outline:hover {
  background: var(--color-surface-alt);
  border-color: var(--color-text-muted);
  color: var(--color-text);
}

.icon {
  flex-shrink: 0;
  width: 14px;
  height: 14px;
}

/* ============================================
   About
   ============================================ */

.about .about-text {
  max-width: 640px;
  margin: 0 auto;
  text-align: center;
  color: var(--color-text-muted);
  font-size: 0.92rem;
  line-height: 1.7;
}

/* ============================================
   Join
   ============================================ */

.join-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
  margin-bottom: 20px;
}

.join-step {
  text-align: center;
  padding: 12px 8px;
}

.join-step-num {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--color-primary);
  color: var(--color-primary-text);
  font-weight: 600;
  font-size: 0.82rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto 8px;
}

.join-step h3 {
  font-size: 0.92rem;
  font-weight: 600;
  margin-bottom: 4px;
}

.join-step p {
  color: var(--color-text-muted);
  font-size: 0.82rem;
}

.join-actions {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 10px;
}

/* ============================================
   Footer
   ============================================ */

.footer {
  padding: 16px 0;
  text-align: center;
  color: var(--color-text-muted);
  font-size: 0.78rem;
  border-top: 1px solid var(--color-border);
}

.footer p {
  margin: 2px 0;
}

.footer a {
  color: var(--color-text-muted);
}

.footer a:hover {
  color: var(--color-primary);
}

/* ============================================
   Responsive
   ============================================ */

/* Tablet and below */
@media (max-width: 768px) {
  .hero {
    padding: 32px 0 28px;
  }

  .hero-logo {
    font-size: 1.75rem;
  }

  .hero-title {
    font-size: 0.95rem;
  }

  .hero-tagline {
    font-size: 0.8rem;
  }

  .hero-decoration {
    font-size: 5rem;
  }

  .section {
    padding: 28px 0;
  }

  .section-title {
    font-size: 1.1rem;
  }

  .section-desc {
    font-size: 0.85rem;
    margin-bottom: 18px;
  }

  .card-grid {
    grid-template-columns: 1fr;
    gap: 14px;
  }

  .card {
    padding: 16px;
  }

  .card-title {
    font-size: 1rem;
  }

  .card-desc {
    font-size: 0.85rem;
  }

  .join-grid {
    grid-template-columns: 1fr;
    gap: 12px;
    margin-bottom: 18px;
  }

  .join-step {
    padding: 12px;
  }

  .join-step-num {
    width: 30px;
    height: 30px;
    font-size: 0.85rem;
  }

  .join-step h3 {
    font-size: 0.9rem;
  }

  .join-step p {
    font-size: 0.8rem;
  }
}

/* Mobile */
@media (max-width: 480px) {
  body {
    font-size: 15px;
  }

  .container {
    padding: 0 20px;
  }

  .hero {
    padding: 28px 0 24px;
  }

  .hero-logo {
    font-size: 1.6rem;
    margin-bottom: 8px;
  }

  .hero-title {
    font-size: 0.92rem;
    margin-bottom: 6px;
  }

  .hero-tagline {
    font-size: 0.78rem;
  }

  .hero-decoration {
    font-size: 4rem;
  }

  .section {
    padding: 24px 0;
  }

  .section-title {
    font-size: 1.05rem;
    margin-bottom: 6px;
  }

  .section-desc {
    font-size: 0.82rem;
    margin-bottom: 16px;
  }

  .card {
    padding: 18px;
    border-radius: var(--radius-md);
  }

  .card-title {
    font-size: 0.98rem;
    margin-bottom: 10px;
  }

  .card-title-en {
    font-size: 0.82rem;
  }

  .card-tags {
    gap: 6px;
    margin-bottom: 12px;
  }

  .tag {
    font-size: 0.7rem;
    padding: 3px 9px;
  }

  .card-desc {
    font-size: 0.85rem;
    margin-bottom: 14px;
    line-height: 1.65;
  }

  /* Touch-friendly buttons */
  .btn {
    padding: 10px 18px;
    font-size: 0.85rem;
    min-height: 44px;
    touch-action: manipulation;
    -webkit-tap-highlight-color: transparent;
  }

  .card-actions {
    gap: 10px;
  }

  .about .about-text {
    font-size: 0.88rem;
    line-height: 1.75;
  }

  .join-step {
    padding: 14px 12px;
  }

  .join-step-num {
    width: 32px;
    height: 32px;
    font-size: 0.88rem;
    margin: 0 auto 10px;
  }

  .join-step h3 {
    font-size: 0.92rem;
    margin-bottom: 6px;
  }

  .join-step p {
    font-size: 0.82rem;
    line-height: 1.6;
  }

  .join-actions {
    gap: 12px;
  }

  .footer {
    padding: 18px 0;
    font-size: 0.75rem;
  }
}

/* Very small screens */
@media (max-width: 360px) {
  .container {
    padding: 0 16px;
  }

  .hero-logo {
    font-size: 1.4rem;
  }

  .hero-title {
    font-size: 0.88rem;
  }

  .card {
    padding: 16px;
  }

  .btn {
    padding: 9px 14px;
    font-size: 0.82rem;
    width: 100%;
    justify-content: center;
  }

  .card-actions {
    flex-direction: column;
  }

  .join-actions {
    flex-direction: column;
    align-items: stretch;
  }

  .join-actions .btn {
    width: 100%;
    justify-content: center;
  }
}

/* Improve touch interaction */
@media (hover: none) and (pointer: coarse) {
  .btn {
    min-height: 44px;
  }

  .card:hover {
    transform: none;
    box-shadow: var(--shadow-card);
  }
}

/* Reduce motion for users who prefer it */
@media (prefers-reduced-motion: reduce) {
  * {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}