Wire up visibility property through the layout and render pipeline: - Add visibility field to LayoutBox, populated from ComputedStyle - Renderer skips painting (background, borders, text, images) for hidden/collapse elements but still recurses into children - Children can override with visibility:visible per CSS spec - display:none already worked (excluded from layout tree); verified 9 new tests: 5 layout tests (display:none exclusion, hidden preserves space, inheritance, visible override, collapse behavior) and 4 render tests (hidden not painted, visible child of hidden parent painted, collapse not painted, display:none not in display list). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>