1. :default CSS pseudo-class

   The `:default` pseudo-class matches checkboxes and radio buttons which are checked by default, `<option>`s with the `selected` attribute, and the default submit button (if any) of a form.

2. :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.

3. indeterminate checkbox

   Indeterminate checkboxes are displayed in a state which is distinct both from being checked or being unchecked. They are commonly used in hierarchical checkboxes to indicate that only some of the checkbox's descendants are checked.