div {width: 300px; height: 200px; background: red;} div:before {content: ''; display: block; width: 300px; height: 150px; background: blue;} div.hoge {width: 150px; height: 29px; background: yellow;} /* classがhogeのdiv */ div .hoge {width: 120px; height: 53px; background: green;} /* divの中にいるclassがhoge */