1. 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)

  2. css selector: `:hover`

  3. css selector: `:hover`: all elements support

  4. css selector: `:hover`: `<a>` element support

  5. css selector: `:hover`: pseudo-element support