代码如下：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style>
form{
width: 1000px;
max-width: 640px;
min-width: 320px;
margin:0 auto;
font-size:20px
}
input{
display: block;
height: 30px;
font-size: 20px;
width: 100%;
margin: 10px 0;
}
</style>
</head>
<body>
<!--表单新增属性-->
<form action="" >
<fieldset>
<legend>表单属性</legend>
<label for="">
用户名：<input type="text" placeholder="例如：小左"
required="required" autocomplete="on" name="username"/>
</label>
邮箱
<input type="email" name="email" />
<label for="">
电话：<input type="tel" pattern="1\d{10}"/>
</label>
<!--上传文件-->
<input type="file" name="file" multiple="multiple" />
<input type="submit" />
</fieldset>
</form>
</body>
</html>