代码示例：（标识：cssref_default_form）
<!DOCTYPE html>
<html>
<head>
<style>
/* 默认的 CSS 值 */
form {
display: block;
margin-top: 0em;
}
</style>
</head>
<body>
<p>默认情况下，form 元素会这样显示：</p>
<form action="/index/demo/form_current.html">
First name: <input type="text" name="FirstName" value="Mickey"><br>
Last name: <input type="text" name="LastName" value="Mouse"><br>
<input type="submit" value="Submit">
</form>
<p>自定义的 form 元素（更改 margin-top）：</p>
<form action="/index/demo/form_current.html" style="margin-top:50px;">
First name: <input type="text" name="FirstName" value="Mickey"><br>
Last name: <input type="text" name="LastName" value="Mouse"><br>
<input type="submit" value="Submit">
</form>
</body>
</html>
