select2/docs/themes/learn2/scss/theme/modules/_buttons.scss

%button {
	display: inline-block;
	padding: 7px 12px;
	&:active {
		margin: 2px 0 -2px 0;
	}
}

@mixin button-color($color) {
	background: $color;
	color: $white;
	box-shadow: 0 3px 0 darken($color, 6%);
	&:hover {
		background: darken($color, 6%);
		box-shadow: 0 3px 0 darken($color, 12%);
		color: $white;
	}
	&:active {
		box-shadow: 0 1px 0 darken($color, 12%);
	}
}