1. :indeterminate CSS pseudo-class

    The `:indeterminate` pseudo-class matches indeterminate checkboxes, indeterminate `<progress>` bars, and radio buttons with no checked button in their radio button group.

  2. css selector: `:indeterminate`: applies to `<input type="checkbox">` elements

  3. css selector: `:indeterminate`: applies to `<progress>` elements

  4. css selector: `:indeterminate`: applies to `<input type="radio">` elements