lovecoding
/
Web1020


			
				
					
						
						
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							<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 100px;
            height: 100px;
            background-color: red;
        }
        .box2{
            border:3px solid black;
        }
        .box3{
            margin-top: 200px;
        }
    </style>
</head>
<body>
    <!-- <div class="box box2"></div> -->
     <div></div>
    <script>
        var oBox = document.getElementsByTagName("div")[0];
        // oBox.setAttribute("class","box");
        // 控制标签类名
        // oBox.className = "box";
        oBox.className = "box box2";

        // var str = "box2";
        // oBox.classList.remove("box2");
        // oBox.classList.add("box2");

        // oBox.classList.replace("box2","box3");

    </script>
</body>
</html>