make login form css

coding a form appropriately

<!DOCTYPE html>
<html>
<head>
	<meta charset="UTF-8">
	<title>ログイン|入稿管理支援システム</title>
	<link rel="stylesheet" type="text/css" href="asset/css/styles.css" />
</head>
<header>
	<p><a href="index.html">Hpscript</a></p>
	<nav>
		<p>入稿管理支援システム</p>
	</nav>
</header>
<body>
    <div id="content">
	<h1>ログイン</h1>
	<form action="cgi-bin/hoge.cgi" method="post">
		<p>
		    ユーザーID:<input type="text" name="login_id" size="20">
		</p>
		<p>
		    パスワード:<input type="text" name="password" size="20">
		</p>
		<p>
		    <input type="submit" value="ログイン">
		</p>
	</form>
	</div>
</body>
</html>

In a sense this is already fine, but i want to it center.

#content {
	margin-top:100px;
	text-align:center;
}
#content h1{
	font-size: 16px;
	margin-bottom:40px;
}

well, finally reaching the point.