Convert CSS index from markdown to HTML
Add ids to CSS index headings
Add CSS Snap Points spec links
Reduce size of spec links
Add CSS Align spec links
Add CSS Backgrounds spec links
Add CSS Break spec links
Add CSS Cascade Spec links
Add CSS Color 3 spec links
Add CSS Color 4 spec links
Add CSS Containment spec links
Add CSS Display spec links
Add CSS Exclusions spec links
Add CSS Flexbox spec links

Note some props are defined in Flexbox and Align.
Add CSS Fonts spec links
Add CSS GCPM spec links
Add CSS Grid spec links
Add CSS Images 3 spec links
Add CSS Images 4 spec links
Add CSS Line Grid spec links