【class】
<!DOCTYPE html>
<html>
<head>
<style type='text/css'>
#test {
padding: 1em;
font-size: 50px;
font-weight: bold;
color: red !important;
}
</style>
</head>
<body>
<div id="test">This is a test</div>
<script type='text/javascript'>
var elem = document.getElementById('test');
elem.style.setProperty( 'color', 'green', 'important' );
</script>
</body>
</html>
