This is a class not a pseudoclass, indicates which button(s) are pressed.
A pseudoclass. Clicking is the main way to trigger an :active state.
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
box-shadow: 0 0 0 3px lightskyblue;
As expected, can have separate hover behavior for .active buttons.
See the Pen
Button .active vs :active by Joyce Robbins (https://codepen.io/jtr13)