Four Colors
Four Colors is the card game everyone's aunt dominates, in clean HTML5: match by colour or number, weaponise the action cards, and empty your hand before up to three computer opponents empty theirs. Don't forget the "1" button on your last card — the game does check.
AI opponents play fast and hold grudges appropriately.
Tip: hoard your colour-change cards past the midgame; early they're convenience, late they're checkmate. The card games tag deals the rest.