/* ============================================================
   叠层归一 · Dieceng Research — Shared Design System
   Dark academic theme with gold/purple/teal accents
   ============================================================ */

:root {
  /* Background layers */
  --bg0: #07080e;
  --bg1: #0c0e18;
  --bg2: #111420;
  --bg3: #181b2e;
  --bg4: #1e2238;

  /* Text */
  --txt: #d6d9e8;
  --h1: #eceef8;
  --muted: #767b99;
  --muted2: #565b73;

  /* Accents */
  --gold: #c8a44e;
  --gold2: #e0c060;
  --purple: #9b87f5;
  --purple2: #b7a6f8;
  --teal: #3dd6c8;
  --teal2: #5ee8dc;
  --blue: #6ea8fe;
  --blue2: #90befe;
  --rose: #f472b6;

  /* Borders */
  --line: rgba(255, 255, 255, 0.07);
  --line2: rgba(255, 255, 255, 0.12);

  /* Sizing */
  --radius: 14px;
  --radius-sm: 8px;
  --radius-lg: 20px;
  --max: 1200px;

  /* Shadows */
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 12px 48px rgba(0, 0, 0, 0.5);

  /* Font */
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Microsoft YaHei", "Noto Sans SC", sans-serif;
  --font-mono: "SF Mono", "Fira Code", "Consolas", monospace;
}

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

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  background: var(--bg0);
  color: var(--txt);
  font-family: var(--font);
  line-height: 1.7;
  min-height: 100vh;
}

a {
  color: inherit;
  text-decoration: none;
}

img {
  max-width: 100%;
  display: block;
}

/* ============================================================
   Typography
   ============================================================ */

h1, h2, h3, h4 {
  color: var(--h1);
  line-height: 1.25;
}

.gradient-text {
  background: linear-gradient(135deg, var(--gold), var(--gold2), var(--teal));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.gradient-text-blue {
  background: linear-gradient(135deg, var(--blue), var(--purple));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

/* ============================================================
   Header / Navigation (shared across all pages)
   ============================================================ */

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(7, 8, 14, 0.78);
  backdrop-filter: blur(16px) saturate(140%);
  -webkit-backdrop-filter: blur(16px) saturate(140%);
  border-bottom: 1px solid var(--line);
  transition: background 0.3s;
}

.header-inner {
  max-width: var(--max);
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 54px;
  gap: 16px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 750;
  font-size: 15.5px;
  color: var(--h1);
  letter-spacing: 0.3px;
  white-space: nowrap;
}

.brand-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--teal);
  box-shadow: 0 0 12px var(--teal), 0 0 24px rgba(61, 214, 200, 0.3);
  animation: brandPulse 3s ease-in-out infinite;
  flex-shrink: 0;
}

@keyframes brandPulse {
  0%, 100% { transform: scale(1); opacity: 1; }
  50% { transform: scale(1.5); opacity: 0.5; }
}

.header-nav {
  display: flex;
  gap: 2px;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.header-nav a {
  padding: 6px 13px;
  border-radius: 7px;
  font-size: 13px;
  color: var(--muted);
  font-weight: 500;
  transition: all 0.2s;
  white-space: nowrap;
}

.header-nav a:hover {
  color: var(--txt);
  background: rgba(255, 255, 255, 0.04);
}

.header-nav a.active {
  color: var(--teal);
  background: rgba(61, 214, 200, 0.08);
  font-weight: 600;
}

/* ============================================================
   Section Headings
   ============================================================ */

.section-hd {
  text-align: center;
  margin-bottom: 36px;
}

.section-hd .kicker {
  display: inline-block;
  padding: 4px 14px;
  border-radius: 20px;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 2px;
  text-transform: uppercase;
  margin-bottom: 12px;
  border: 1px solid var(--line);
  color: var(--teal);
  background: rgba(61, 214, 200, 0.06);
}

.section-hd h2 {
  font-size: clamp(22px, 3.5vw, 32px);
  font-weight: 800;
  margin-bottom: 10px;
  letter-spacing: -0.3px;
}

.section-hd p {
  color: var(--muted);
  font-size: 15px;
  max-width: 560px;
  margin: 0 auto;
}

/* ============================================================
   Container
   ============================================================ */

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

.section {
  padding: 60px 0;
}

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

.card {
  background: var(--bg2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 28px 24px;
  transition: all 0.25s;
}

.card:hover {
  border-color: var(--line2);
  transform: translateY(-3px);
  box-shadow: var(--shadow);
}

.card-clickable {
  cursor: pointer;
  display: block;
}

.card-clickable:hover {
  border-color: var(--teal);
  box-shadow: 0 8px 32px rgba(61, 214, 200, 0.08);
}

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

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 22px;
  border-radius: 8px;
  font-size: 14px;
  font-weight: 600;
  border: 1px solid var(--line);
  background: var(--bg2);
  color: var(--txt);
  cursor: pointer;
  transition: all 0.2s;
}

.btn:hover {
  border-color: var(--teal);
  background: rgba(61, 214, 200, 0.06);
  color: var(--teal);
}

.btn-primary {
  background: linear-gradient(135deg, var(--teal), #2aada0);
  border-color: transparent;
  color: #07080e;
  font-weight: 700;
}

.btn-primary:hover {
  box-shadow: 0 4px 20px rgba(61, 214, 200, 0.3);
  color: #07080e;
}

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

.site-footer {
  text-align: center;
  padding: 36px 24px;
  color: var(--muted2);
  font-size: 13px;
  border-top: 1px solid var(--line);
  line-height: 1.8;
}

.site-footer a {
  color: var(--teal);
  transition: color 0.2s;
}

.site-footer a:hover {
  color: var(--teal2);
}

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

@media (max-width: 768px) {
  .header-inner {
    padding: 0 16px;
    height: 48px;
    gap: 8px;
  }
  .brand {
    font-size: 14px;
  }
  .header-nav a {
    font-size: 11.5px;
    padding: 5px 9px;
  }
  .section {
    padding: 40px 0;
  }
  .container {
    padding: 0 16px;
  }
}

@media (max-width: 520px) {
  .header-nav {
    gap: 0;
  }
  .header-nav a {
    font-size: 10.5px;
    padding: 4px 6px;
  }
}