【class】
<!DOCTYPE html>
<html>
<head>
<style type='text/css'>
.red:not (.yellow ) {
color: red;
}
.yellow {
background-color: yellow;
}
</style>
</head>
<body>
<div class="red yellow">Glee's awesome!</div>
<div class="red">Glee's awesome!</div>
</body>
</html>
