@media (max-width: 900px) {
  .site-header { position: relative; }
  .site-header nav.mobile-open {
    position: absolute;
    z-index: 20;
    display: grid;
    top: 68px;
    left: 16px;
    right: 16px;
    padding: 18px;
    background: #fff;
    border: 1px solid var(--line);
    border-radius: 16px;
    box-shadow: var(--shadow);
  }
}