/* ============================================================
   导航（含移动端汉堡菜单）
   ============================================================ */
.nav {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 100;
  padding: 18px var(--gutter);
  display: flex;
  align-items: center;
  justify-content: space-between;
  backdrop-filter: blur(12px) saturate(1.4);
  -webkit-backdrop-filter: blur(12px) saturate(1.4);
  background: color-mix(in oklch, var(--bg) 70%, transparent);
  border-bottom: 1px solid var(--border);
  transition: background var(--dur) var(--ease), border-color var(--dur) var(--ease);
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: 12px;
  font-family: var(--font-mono);
  font-size: 14px;
  font-weight: 500;
  letter-spacing: 0.04em;
}

.nav-logo .dot {
  width: 8px; height: 8px;
  background: var(--accent);
  border-radius: 50%;
  box-shadow: 0 0 12px var(--accent-glow);
  animation: pulse 2.4s ease-in-out infinite;
}

.nav-links {
  display: flex;
  gap: 4px;
  list-style: none;
  align-items: center;
}

.nav-links a {
  padding: 8px 14px;
  font-size: 13px;
  font-weight: 500;
  color: var(--fg-soft);
  border-radius: 999px;
  letter-spacing: 0.02em;
  position: relative;
  transition: color 0.2s var(--ease), background 0.2s var(--ease);
}

.nav-links a:hover {
  color: var(--fg);
  background: var(--surface);
}

.nav-actions {
  display: flex;
  gap: 8px;
  align-items: center;
}

.theme-toggle {
  width: 38px; height: 38px;
  border-radius: 50%;
  border: 1px solid var(--border-strong);
  background: var(--surface);
  display: grid;
  place-items: center;
  transition: transform 0.3s var(--ease), background 0.3s var(--ease);
  overflow: hidden;
  position: relative;
}

.theme-toggle:hover { transform: rotate(180deg); }
.theme-toggle:active { transform: scale(0.92); transition-duration: 0.1s; }

.theme-toggle svg {
  width: 16px; height: 16px;
  stroke: var(--fg);
  transition: opacity 0.3s var(--ease), transform 0.3s var(--ease);
  position: absolute;
}

.theme-toggle .sun { opacity: 0; transform: rotate(-90deg) scale(0.5); }
.theme-toggle .moon { opacity: 1; transform: rotate(0) scale(1); }

[data-theme="light"] .theme-toggle .sun { opacity: 1; transform: rotate(0) scale(1); }
[data-theme="light"] .theme-toggle .moon { opacity: 0; transform: rotate(90deg) scale(0.5); }

.nav-cta {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 9px 18px;
  background: var(--accent);
  color: var(--accent-fg);
  font-size: 13px;
  font-weight: 600;
  border-radius: 999px;
  letter-spacing: 0.02em;
  transition: transform 0.3s var(--ease), box-shadow 0.3s var(--ease);
}

.nav-cta:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 24px var(--accent-glow);
}

.nav-cta:active {
  transform: translateY(0);
  box-shadow: 0 4px 12px var(--accent-glow);
  transition-duration: 0.1s;
}

/* 移动端汉堡菜单 — 默认隐藏，< 768px 显示 */
.nav-menu-toggle {
  display: none;
  width: 38px; height: 38px;
  border-radius: 50%;
  border: 1px solid var(--border-strong);
  background: var(--surface);
  place-items: center;
  position: relative;
  cursor: pointer;
}

.nav-menu-toggle svg {
  width: 16px; height: 16px;
  stroke: var(--fg);
  fill: none;
  stroke-width: 2;
  stroke-linecap: round;
  position: absolute;
  transition: opacity 0.25s var(--ease), transform 0.25s var(--ease);
}

.nav-menu-toggle .icon-open { opacity: 1; transform: rotate(0) scale(1); }
.nav-menu-toggle .icon-close { opacity: 0; transform: rotate(-90deg) scale(0.5); }

.nav-menu-toggle[aria-expanded="true"] .icon-open { opacity: 0; transform: rotate(90deg) scale(0.5); }
.nav-menu-toggle[aria-expanded="true"] .icon-close { opacity: 1; transform: rotate(0) scale(1); }

.nav-overlay {
  position: fixed;
  inset: 0;
  z-index: 99;
  background: color-mix(in oklch, var(--bg) 96%, transparent);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 80px var(--gutter) 40px;
  opacity: 0;
  visibility: hidden;
  transform: translateY(-10px);
  transition: opacity 0.3s var(--ease), transform 0.3s var(--ease), visibility 0.3s;
}

.nav-overlay.open {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.nav-overlay a.overlay-link {
  font-family: var(--font-display);
  font-size: clamp(28px, 6vw, 44px);
  font-weight: 500;
  color: var(--fg);
  letter-spacing: -0.02em;
  padding: 8px 20px;
  line-height: 1.2;
  transition: color 0.2s var(--ease);
}

.nav-overlay a.overlay-link:hover { color: var(--accent); }

.nav-overlay .overlay-actions {
  display: flex;
  gap: 12px;
  margin-top: 32px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}

.nav-overlay .overlay-actions .btn { font-size: 14px; }