CSS

css active

#id{
  background-color: red;
}
#id:active{
  background-color: Green;
}
/* note: Active doesn't mean click,
   it's when you press and hold the left mouse button.
   so when you press and hold, the background will change from red to green,
   and when you release the mouse it will change back to red   */

/* useful for scrollbar */
#container::-webkit-scrollbar-thumb:active{
	background-color: /*  colour  */;
}

button active css

form :active {
  color: red;
}

form button:active {
  background: black;
}

css active button

button.selected{
 backround:red;
}