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<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
<ul class="ul">
<li class="red">列表项01</li>
<li>列表项02</li>
<li class="green">列表项03</li>
<li>列表项04</li>
<li class="yellow">列表项05</li>
</ul>
</body>
<script>
var red = document.getElementsByClassName('red');
// console.log(red);
red[0].style.background = 'red'
//改方法不仅可以在document对象上调用，也可以在元素上调用，一般是在父元素上调用
document.getElementsByClassName('ul').item(0)
.getElementsByClassName('green').item(0)
.style.background = 'green'
//class支持多值
var yellow = document.getElementsByClassName('yellow')[0];
yellow.style.background = 'yellow';
yellow.style.fontSize = '1.5rem'
</script>
</html>
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