Performance: Missing style computation cache

Description

Style computation calls matchRules() for every element without caching results, causing redundant selector matching.

Location

• style/style.go:205-227 - matchRules()
• style/style.go:52+ - ApplyStyles() (walks entire DOM tree)

Problem

When multiple elements have identical characteristics (same tag, classes, ancestors), the style computation is repeated from scratch. This is common in:

• List items (<li>)
• Table cells (<td>)
• Repeated structural patterns

Suggested Improvements

1. Cache matched rules by selector signature - Hash element characteristics and cache matching results
2. Inherit cached styles - Elements with identical parent chains can share style computation
3. Index rules by applicability - Pre-filter rules that could never match based on tag/class
4. Use computed style caching - Store final computed styles and reuse for similar elements

Example Cache Key

type StyleCacheKey struct {
    TagName   string
    Classes   string  // sorted, comma-joined
    ID        string
    ParentKey *StyleCacheKey
}

Impact

Pages with repeated structures (tables, lists, cards) would see significant speedup during initial style computation.

Start by reading style/style.go:52+ to understand ApplyStyles and style/style.go:205-227 to trace matchRules. Compare the suggested cache-key and rule-indexing approaches against repeated list and table structures. Done means preserving style results while avoiding redundant selector matching and demonstrating the performance improvement.