.nav{position:sticky;top:0;z-index:40}.nav-inner{min-height:56px}.nav-brand{border:1px solid var(--color-border);padding:var(--space-2) var(--space-3);background-color:var(--color-surface);text-decoration:none}.nav-brand span:nth-child(1){letter-spacing:0.18em}.nav-brand span:nth-child(2){max-width:260px}.nav-menu a,.nav-meta-item{position:relative;padding-bottom:2px}.nav-menu a::after,.nav-meta-item::after{content:"";position:absolute;left:0;bottom:0;width:0;height:1px;background-color:var(--color-primary);transition:width var(--transition-fast)}.nav-menu a:hover::after,.nav-meta-item:hover::after{width:100%}.nav-menu a[aria-current="page"]::after{width:100%}.highlight-primary{color:var(--color-primary)}.nav-toggle{background-color:var(--color-surface)}.nav-toggle span{transition:transform var(--transition-fast),opacity var(--transition-fast)}.nav-toggle.is-active span:nth-child(1){transform:translateY(5px) rotate(45deg)}.nav-toggle.is-active span:nth-child(2){opacity:0}.nav-toggle.is-active span:nth-child(3){transform:translateY(-5px) rotate(-45deg)}.nav-mobile{border-top:1px solid var(--color-border)}.nav-mobile a{background-color:var(--color-surface)}.nav-mobile a:hover{background-color:var(--gray-100)}@media (max-width:720px){.nav{background-color:var(--color-surface)}.nav-inner{gap:var(--space-2)}.nav-brand{flex:1}}