菜鸟教程在线编辑器

AI 编程工具
 
                <!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"> 
<title>菜鸟教程(runoob.com)</title> 
<style>
input:required
{
	background-color: yellow;
}
</style>
</head>
<body>

<h3>A demonstration of the :required selector.</h3>

<p>An optional input element:<br><input></p>

<p>A required input element:<br><input required></p>

<p> :required选择器选择表单元素有“需要”属性.</p>

</body>
</html>
              