Modern CSS Feature Support For Shadow DOM

Feature List
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Last Updated: April 2, 2026

Changelog for: Popover

January 13, 2026

Began tracking feature

Support Definition Keys

Support Categories

Supported Per Spec
Acceptable Support
Use With Caution
Not Recommended

Functional Support Key

Unsupported: no support
Low: partial, insufficient support
Progressing: open issues/bugs for essential features
Critical: essential features for most expected use cases are supported
Supported: all expected features are supported

Shadow DOM Usage Key

Light DOM Priority: feature must be defined in the light DOM, but can be accessed in the shadow DOM
Cross-Context: feature can be defined and used within both light and shadow DOM
Cross-Boundary: feature can access light DOM definitions from within shadow DOM

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