.site-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: #faf7f0;
  border-bottom: 1.5px solid var(--color-divider);
  box-shadow: 0 1px 0 rgba(0,0,0,0.04);
}

.site-nav__inner {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: var(--space-3) var(--space-5);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
}

.site-nav__back {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 4px 10px;
  border: 1.5px solid var(--color-primary-light);
  border-radius: var(--radius-full);
  color: var(--color-primary-dark);
  font-size: var(--text-sm);
  font-weight: 500;
  transition: all var(--duration-fast) var(--ease);
  background: var(--color-surface);
  white-space: nowrap;
}
.site-nav__back:hover {
  background: var(--color-primary);
  color: #fefcf6;
  border-color: var(--color-primary);
}
@media (max-width: 767px) {
  /* 手机端: 汉堡菜单已含"首页"链接, 隐藏独立返回按钮避免布局溢出 */
  .site-nav__back { display: none; }
}

.site-nav__brand {
  font-family: var(--font-serif);
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-primary);
  display: flex;
  align-items: center;
  gap: var(--space-2);
}
.site-nav__brand-mark {
  width: 28px; height: 28px;
  background: var(--color-primary);
  border-radius: 50%;
  display: inline-block;
  position: relative;
}
.site-nav__brand-mark::after {
  content: "";
  position: absolute;
  top: 8px; left: 6px;
  width: 16px; height: 12px;
  background: var(--color-accent);
  border-radius: 50% 50% 50% 50% / 60% 60% 40% 40%;
}

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

.site-nav__link {
  position: relative;
  font-size: var(--text-sm);
  color: var(--color-text);
  padding: var(--space-2) 0;
  transition: color var(--duration-fast) var(--ease);
}
.site-nav__link:hover { color: var(--color-accent); }
.site-nav__link--active {
  color: var(--color-primary);
  font-weight: 500;
}
.site-nav__link--active::after {
  content: "";
  position: absolute;
  left: 0; right: 0; bottom: -1px;
  height: 2px;
  background: var(--color-accent);
}

.site-nav__toggle {
  display: none;
  width: 40px; height: 40px;
  align-items: center;
  justify-content: center;
  background: var(--color-primary);
  border: 1.5px solid var(--color-primary);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease);
}
.site-nav__toggle:hover,
.site-nav__toggle:active {
  background: var(--color-primary-dark);
  border-color: var(--color-primary-dark);
}
.site-nav__toggle span,
.site-nav__toggle span::before,
.site-nav__toggle span::after {
  content: "";
  display: block;
  width: 20px; height: 2.5px;
  background: #fefcf6;
  position: relative;
  transition: transform var(--duration) var(--ease);
  border-radius: 1px;
}
.site-nav__toggle span::before { position: absolute; top: -7px; }
.site-nav__toggle span::after { position: absolute; top: 7px; }

@media (max-width: 767px) {
  .site-nav__toggle { display: flex; }
  .site-nav__menu {
    position: fixed;
    inset: 56px 0 0 0;
    background: var(--color-surface);
    flex-direction: column;
    align-items: stretch;
    padding: var(--space-5);
    gap: 0;
    transform: translateX(100%);
    transition: transform var(--duration) var(--ease);
    border-top: 1px solid var(--color-divider);
  }
  .site-nav__menu.is-open { transform: translateX(0); }
  .site-nav__link {
    padding: var(--space-4) 0;
    font-size: var(--text-base);
    border-bottom: 1px solid var(--color-divider);
  }
  .site-nav__link--active::after { display: none; }
}