:focus-visible CSS pseudo-class

The `:focus-visible` pseudo-class applies while an element matches the `:focus` pseudo-class, and the UA determines via heuristics that the focus should be specially indicated on the element (typically via a “focus ring”).

:focus-within CSS pseudo-class

The `:focus-within` pseudo-class matches elements that either themselves match `:focus` or that have descendants which match `:focus`.

CSS 2.1 selectors

Basic CSS selectors including: `*` (universal selector), `>` (child selector), `:first-child`, `:link`, `:visited`, `:active`, `:hover`, `:focus`, `:lang()`, `+` (adjacent sibling selector), `[attr]`, `[attr="val"]`, `[attr~="val"]`, `[attr|="bar"]`, `.foo` (class selector), `#foo` (id selector)

css selector: `:focus`

css selector: `:focus-visible`