Sliding Tab Indicator

Tab underline slides between tabs.

.tabs { display:flex; gap:0; position:relative; background:#1c1c1f; border-radius:8px; padding:4px; }
.tabs button { flex:1; padding:8px 16px; background:none; border:none; color:#999; cursor:pointer; border-radius:6px; transition:color 0.2s; z-index:1; }
.tabs button.active { color:white; background:#333; }