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求助为什么我不能编辑那两个button

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
    *{margin:0;padding:0;}
    
    .container{
        
        width:220px;
        height:350px;
        background:#ebf2fa;
     
    }
    .form_m{
        padding:15px;
         
    }
    .input_text{
         
        display:block;
        width:180px;
        height:28px;
        margin-top:12px;
        border-radius:4px;/*圆角矩形*/
        text-indent:20px;/*文字缩进，需块元素或内联块元素*/
       
    }
     
     
    p{
        margin-top:10px;
        height:50px;
        font-size:13px;
    }
    p label{
         
        vertical-align: top;
            
    }
    p a{
        
        text-decoration:none;
        float:right;
         
    }
 
    }
    .btn{
    width:200px;
    height:20px;
    background:url(http://img1.sycdn.imooc.com//539a972b00013e9102280177.jpg)
    }
     
</style>
</head>
 
<body>
<div class="container">
    <form class="form_m">
        <input class="input_text" placeholder="邮箱/手机号/用户名" type="text"/>
        <input class="input_text" placeholder ="请输入密码"type="password"/>
        <p>
            <input class="checkbox" type="checkbox" id="1"/>
            <label for="1">下次自动登陆</label>
            <a href="javascript:;">忘记密码?</a>
        </p>
        <input  class="btn" type="submit" value="登陆"/>
        <hr/> 
        <input class="btn" type="button" value="注册"/>
    </form>
</div>
 
</body>
</html>