<html><head><style> #myDIV { border: 1px solid black; width: 300px; height: 300px;}</style></head><body><h1>用 JavaScript 改变右边框</h1><p>点击“试一试”按钮更改 DIV 元素的 border-right 属性：</p><button onclick="myFunction()">试一试</button><div id="myDIV"> <h1>Hello</h1></div><script>function myFunction() { document.getElementById("myDIV").style.borderRight = "5px dotted lightblue";}</script></body></html>