/* 内容原型页公共顶栏：posts / moments / albums 共用同一视觉 */
.site-top {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  justify-content: space-between;
  box-sizing: border-box;
  /* 站点框 = 栏目页标题块与内容同宽（tokens.css 的 --page-frame），头部与页面左右缘永远对齐 */
  width: var(--page-frame);
  margin-inline: auto;
  padding: var(--space-4) 0;
  background: color-mix(in srgb, var(--bg) 84%, transparent);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-subtle);
}

.site-brand {
  padding: 0;
  border: 0;
  background: none;
  color: var(--text-primary);
  font-family: var(--font-display);
  font-size: 1.15rem;
  font-weight: 600;
  cursor: pointer;
}

.site-top nav {
  display: flex;
  align-items: center;
  gap: var(--space-5);
}

.site-top nav button:not(.theme-toggle) {
  border: 0;
  border-bottom: 1px solid transparent;
  background: none;
  color: var(--text-secondary);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  cursor: pointer;
}

.site-top nav button.is-active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}

.site-top .theme-toggle {
  position: relative;
  flex: none;
  box-sizing: border-box;
  width: 52px;
  height: 28px;
  padding: 0;
  border: 1px solid var(--border-default);
  border-radius: var(--radius-pill);
  background: var(--bg-inset);
  cursor: pointer;
}

.site-top .theme-toggle-track {
  position: absolute;
  inset: 0;
}

.site-top .theme-toggle-thumb {
  position: absolute;
  top: 2px;
  left: 2px;
  display: grid;
  place-items: center;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: var(--bg-elevated);
  box-shadow: var(--shadow-sm);
  color: var(--accent);
  transition: transform 0.3s var(--ease-standard);
}

.site-top .theme-toggle.is-dark .theme-toggle-thumb {
  transform: translateX(24px);
}

@media (max-width: 640px) {
  .site-top {
    width: 100%;
    padding-inline: var(--space-4);
  }
}