- Collapse the 10 theme cards into 5 pairs: light swatches top row, dark bottom row - Dark mode toggle in settings and topbar (sun/moon inline SVG) - Toggling dark mode switches to the other variant of the selected pair - Persist pair id in localStorage palette-theme, dark flag in palette-dark - Head script resolves base+dark to variant; URL ?theme= accepts both ids and wins - Settings gear highlights like nav tabs on /settings - PALETTE_DEFAULT_DARK env var sets server default dark state (default on) - Server-side resolution helpers + tests