<!DOCTYPE html>
<html>
<head>
<style>
fieldset:invalid { border: 2px solid red;
background-color: beige;
}
input:invalid { border: 2px solid red;
background-color: beige;
}
</style>
</head>
<body>
<h1>:invalid 实例</h1>
<p>尝试输入一个合法的电子邮件地址，看看样式如何消失。</p>
<p>同时选择一个单选按钮，看看样式如何消失。</p>
<p>尝试输入一个合法的数字，看看样式如何消失。</p>
<form>
<label for="name">姓名：</label><br>
<input id="name" name="name" type="text" /><br>
<label for="email">邮箱：</label><br>
<input id="email" name="email" type="email" value="supportEmail" />
<br><br>
<fieldset>
<legend>选择性别：</legend>
<label><input name="gender" type="radio" value="male" required> 男</label>
<label><input name="gender" type="radio" value="female" required> 女</label>
<label><input name="gender" type="radio" value="other" required> 其他</label>
</fieldset>
<p>请输入一个介于 1 到 10 之间的数字：<input type="number" min="1" max="10" value="17"></p>
</form>
</body>
</html>