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<html><head><meta charset="UTF-8"><title></title><style>*{margin:0; padding:0;}div{margin:0 auto;width:500px;height:300px;line-height:300px;background-color:red;text-align:center;}.red{background-color:red;}.blue{background-color:blue;}button{/*display:inline-block;*/width:100px;}</style></head><body><div class="red"><button onclick="hello()">改变背景颜色</button><!--<a href="javascript:alert('hello')">改变背景颜色</a>--></div></body><script type="text/javascript">let divs=document.getElementsByTagName('div')function hello(){//找到需要改变背景颜色的容器if(divs[0].className=='red'){divs[0].className='blue'}else{divs[0].className='red'}}</script>
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<html><head><meta charset="UTF-8"><title>固定定位+锚记.html</title><style type="text/css">.main{height: 3000px;padding: 1500px 0;}.img{position: fixed;right: 0;bottom: 0;}</style></head><body><!--网页高度三屏 --><div class="main"><h1 id="top">我是顶部</h1><div class="img"><a href="#top"><img src="img/回到顶部.png"></a></div><!--点击图片，回到顶部--></div></body>
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