.masthead {
    position: sticky;
    top: 0;
    z-index: 100;
    background: var(--bg);
    transition: transform 0.3s ease;
    will-change: transform;
}

.masthead--hidden {
    transform: translateY(-100%);
}

@media (prefers-reduced-motion: reduce) {
    .masthead { transition: none; }
}