1. CSS Nesting

    CSS nesting provides the ability to nest one style rule inside another, with the selector of the child rule relative to the selector of the parent rule. Similar behavior previously required a CSS pre-processor.

  2. :optional CSS pseudo-class

    The `:optional` pseudo-class matches form inputs (`<input>`, `<textarea>`, `<select>`) which are not `:required`.

  3. htmlselectelement api: required

  4. css selector: `:first-child`: matches elements with no parent

  5. css selector: `:last-child`: matches elements with no parent

  6. css selector: `:nth-child()`: matches elements with no parent

  7. css selector: `:nth-last-child()`: matches elements with no parent

  8. css selector: `:only-child`: matches elements with no parent

  9. css selector: `:required`

  10. html element: select: required