CSS resource loading: support #74

Phase 8 — Resource Loading + Character Encoding + Real Page Loading#

Implement loading of external CSS stylesheets referenced by <link rel="stylesheet"> elements.

Requirements#

• After HTML parsing, scan the DOM for <link rel="stylesheet" href="..."> elements
• Resolve the href attribute against the document's base URL
• Fetch the stylesheet using the ResourceLoader
• Parse the fetched CSS text using the css crate parser
• Merge external stylesheet rules with inline <style> rules in proper cascade order
• Handle @import rules (fetch and parse imported stylesheets, with depth limit to prevent cycles)
• Respect media attribute on <link> (basic: screen, all)
• Handle type="text/css" attribute (default if omitted)

Integration Points#

• html crate: extract <link> elements from DOM after tree building
• url crate: resolve relative URLs
• encoding crate: decode CSS text with correct encoding
• css crate: parse stylesheet text
• style crate: merge rules into cascade

Acceptance Criteria#

• External stylesheets are fetched and parsed
• Rules from external sheets participate in cascade with correct origin/order
• Relative URLs in href are resolved correctly
• @import is followed (with cycle/depth protection, max depth 5)
• Missing/failed stylesheet loads are handled gracefully (no crash)
• No external dependencies, no unsafe
• Unit tests with mock/constructed scenarios

Dependencies#

Depends on: Resource loader, CSS parser (already complete)