问题遇到的现象和发生背景
vscode显示这个是哪个扩展没安装吗？
用代码块功能插入代码，请勿粘贴截图
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>多栏布局</title>
<link rel="stylesheet" href="css/DivTest04.css">
</head>
<body>
<div id="back">
<div id="top">top</div>
<div id="center">
<div id="left">left</div>
<div id="right">
<iframe src="cat.html" frameborder="0" id="showCat"></iframe>
</div>
</div>
<div id="foot">foot</div>
</div>
</body>
</html>
