.site-header {
    position: sticky;
    top: 0;
    z-index: 100;
    background-color: var(--color-brown);
    border-bottom: 1px solid rgba(195, 165, 95, 0.5);
    /* モバイルナビの absolute 配置の包含ブロックとして明示 */
    isolation: isolate;
}
.site-header__inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}
.site-header__logo {
    font-family: var(--font-serif);
    font-size: var(--text-sm);
    font-weight: 400;
    letter-spacing: 0.15em;
    color: var(--color-offwhite);
    text-transform: uppercase;
}
.site-header__nav-list {
    display: flex;
    gap: var(--space-md);
    list-style: none;
}
.site-header__nav-list a {
    font-family: var(--font-serif);
    font-size: var(--text-sm);
    letter-spacing: 0.1em;
    color: var(--color-offwhite);
    position: relative;
    padding-bottom: 2px;
}
.site-header__nav-list a::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 1px;
    background-color: var(--color-gold);
    transition: width var(--transition-base);
}
.site-header__nav-list a:hover::after { width: 100%; }

/* ハンバーガー */
.site-header__hamburger {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 4px;
    min-width: 44px;
    min-height: 44px;
    align-items: center;
    justify-content: center;
}
.site-header__hamburger span {
    display: block;
    width: 24px;
    height: 1px;
    background-color: var(--color-offwhite);
    transition: transform var(--transition-base), opacity var(--transition-base);
}
.site-header__hamburger.is-open span:nth-child(1) { transform: translateY(6px) rotate(45deg); }
.site-header__hamburger.is-open span:nth-child(2) { opacity: 0; }
.site-header__hamburger.is-open span:nth-child(3) { transform: translateY(-6px) rotate(-45deg); }

/* モバイルナビ */
@media (max-width: 767px) {
    .site-header__hamburger { display: flex; }
    .site-header__nav {
        display: none;
        position: absolute;
        top: 64px;
        left: 0;
        right: 0;
        background-color: var(--color-brown);
        padding: var(--space-md);
        border-top: 1px solid rgba(195, 165, 95, 0.5);
    }
    .site-header__nav.is-open { display: block; }
    .site-header__nav-list {
        flex-direction: column;
        gap: var(--space-sm);
    }
    .site-header__nav-list a { font-size: var(--text-base); }
}