Performance: O(n²) selector matching with descendant combinators

Description

CSS selector matching in style/style.go has O(n²) complexity when dealing with descendant selectors on large documents.

Location

• style/style.go:205-275 - matchRules(), matchesSelector(), matchesDescendant()

Problem

1. matchRules() iterates over ALL rules × ALL selectors for every element
2. matchesDescendant() recursively walks ancestors for each selector with descendant combinators
3. For each element, this triggers O(ancestors) walks per rule

Complexity: O(elements × rules × selectors × tree_depth)

Suggested Improvements

1. Index selectors by tag name/class/ID - Create lookup maps during stylesheet parsing to quickly filter rules that could match
2. Cache selector matching results - Memoize matches for identical elements
3. Bloom filter for ancestors - Use bloom filters to quickly reject non-matching descendant selectors
4. Right-to-left matching with early exit - Already partially implemented, but could be optimized further

Impact

Large pages like Hacker News (many <tr>, <td> elements) will experience significant slowdowns during style computation.