- Add Sticky variant to Position enum and parse "sticky" keyword - Sticky elements participate in normal flow (like relative positioning) - Store sticky_constraint rect on LayoutBox (parent's content area) - Compute sticky paint-time offset in render crate based on scroll state - Support top stickiness with containing block constraint clamping - Update scroll container reference point tracking through paint recursion - Add tests: parsing, normal flow layout, constraint rect, scroll sticking, and parent constraint behavior Implements issue 3mhlhoituxu2u Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>