Modern CSS in 0.60

Historical 0.60 note

Use Modern CSS in 1.0 for current application guidance.

The 0.60 checkout completes the 0.59 modern CSS authority with the custom theme platform. The existing compiler, cascade, token markers, and default_styles=False behavior remain authoritative.

Styling completion

0.60 adds absolute colors with deterministic sRGB fallbacks, immutable ThemeSpec and ThemePatch authoring, registry-derived validation profiles, accessibility mappings, bounded recipe families, server-first theme preference markers, and a read-only Explorer Theme Lab. Brand, ToastHost, ConnectorFlow, and ScrollRegion expose finite presentation contracts that work without application CSS and retain print, reduced-motion, forced-color, and feature-off fallbacks.

See What's new in 0.60 and the upgrade guide for the public authoring and compatibility path.