This is a class not a pseudoclass, indicates which button(s) are pressed.
20.1.2:active
A pseudoclass. Clicking is the main way to trigger an :active state.
20.1.3:focus
A pseudoclass. Mainly used for tabbing. Clicking may focus a button but not always. A box shadow such as box-shadow: 0 0 0 3px lightskyblue; is a good choice
20.1.4:hover
As expected, can have separate hover behavior for .active buttons.