/* ===== 站点头部 ===== */
.site-header {
    position: relative;
    z-index: 50;
    border-bottom: 1px solid rgba(226, 232, 240, .6);
    background: rgba(255, 255, 255, .85);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
}
.site-header.is-sticky {
    position: sticky;
    top: 0;
    box-shadow: 0 4px 24px rgba(15, 23, 42, .06);
}
.site-header__inner {
    display: flex;
    align-items: center;
    min-height: var(--header-height);
    gap: 28px;
}
.site-logo { flex: 0 0 140px; }
.site-logo img { width: 140px; height: auto; object-fit: contain; }

/* 导航 */
.site-nav { flex: 1; min-width: 0; }
.site-nav__list {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: clamp(12px, 1.6vw, 28px);
    white-space: nowrap;
}
.site-nav__item { position: relative; }
.site-nav__item > a {
    display: inline-flex;
    min-height: var(--header-height);
    align-items: center;
    color: var(--color-heading);
    font-size: 15px;
    font-weight: 600;
    position: relative;
    transition: color var(--transition);
}
.site-nav__item > a::after {
    content: "";
    position: absolute;
    bottom: 18px;
    left: 50%;
    transform: translateX(-50%);
    width: 0;
    height: 2px;
    border-radius: var(--radius-full);
    background: var(--gradient-accent);
    transition: width var(--transition);
}
.site-nav__item > a:hover,
.site-nav__item > a.is-current { color: var(--color-secondary); }
.site-nav__item > a:hover::after,
.site-nav__item > a.is-current::after { width: 24px; }

/* 下拉菜单 */
.site-nav__submenu {
    position: absolute;
    top: calc(100% - 8px);
    left: 50%;
    width: 200px;
    padding: 12px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    background: #fff;
    box-shadow: var(--shadow-card);
    opacity: 0;
    pointer-events: none;
    transform: translate(-50%, 8px);
    transition: opacity var(--transition), transform var(--transition);
}
.site-nav__item:hover .site-nav__submenu,
.site-nav__item:focus-within .site-nav__submenu {
    opacity: 1;
    pointer-events: auto;
    transform: translate(-50%, 0);
}
.site-nav__submenu a {
    display: block;
    padding: 9px 12px;
    border-radius: var(--radius-xs);
    font-size: 14px;
    color: var(--color-text);
    transition: background var(--transition), color var(--transition);
}
.site-nav__submenu a:hover { background: var(--color-bg-light); color: var(--color-primary); }

/* 头部操作 */
.site-header__actions { display: flex; align-items: center; gap: 12px; }
.menu-toggle, .menu-close { display: none; background: transparent; color: var(--color-heading); }
.mobile-navigation { display: none; }