Pseudo-classes and states

Pseudo-classes match an element when its state applies. For example:

button.primary:hover { background: #585b70; }
button:disabled { opacity: 0.5; }

State	Matches
:hover	The element under the pointer, according to interactive hit testing. Painted parts use their own hit area.
:focus	The focused element.
:pressed, :active	A pressed element; :active is an alias.
:selected, :checked, :indeterminate	Applicable selection or checked state.
:expanded, :invalid, :busy	Applicable expanded, validation, or busy state.
:enabled, :disabled	Applicable enabled state.
:root	The root element.

A state only matches where the widget exposes it. See selectors for widget types and painted parts.