How to change button selector background that the default is blue

Answer 1

button {
background-color: blue;
}

Answer 2

I want, when it is off (non-active) the bg is default and when it is on clicked or dragged the bg is changed

Answer 3

maybe

button:hover{
background-color: blue;
}

Answer 4

html:
<button id="blueBtn" onclick="addClass()">Submit</button>
<script>
function addClass() {
const btn = document.getElementById('blueBtn');
btn.classList.add(bgBlue);
}
</script>

css:
.bgBlue {
background-color: blue;
}