Define :modal pseudo-class and start using it

[nt1m]

• At least two implementers are interested (and none opposed):
  • Implemented in all browsers
• Tests are written and can be reviewed and commented upon at:
  • https://wpt.fyi/results/css/selectors/modal-pseudo-class.html?label=master&label=experimental&aligned&q=css%2Fselectors%2Fmodal
• Implementation bugs are filed:
  • N / A, already implemented everywhere
• MDN issue is filed: N / A, already exists: https://developer.mozilla.org/en-US/docs/Web/CSS/:modal

(See WHATWG Working Mode: Changes for more details.)

---

/rendering.html ( diff )
/semantics-other.html ( diff )

[nt1m]

cc @whatwg/css

[mfreed7]

LGTM, thanks for defining this.