CSS，求赐教！！！
现在有个页面是这样的 代码如下， 有这么几个需求
1，<div id="main_bg"> 上下左右居中于<div id="main_bg"> 并且两个div 会随着浏览器的大小 自动相对变化
2，<div id="main_bg">这个div有输入框，输入框的大小可以随着输入文字的长度改变，默认情况下宽 300px
麻烦大神赐教，如何修改当前的页面！
CSS
<!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>
{$PLUGIN_TITLE}
</title><script language="php">
$templateVersion = 2; // Template version
// $fieldRowLayout determines the layout of the form fields
// Options are 'fieldset' and 'table'
// fieldset: displays fieldnames above the input box
// table: displays fieldnames in front of the input box
$fieldRowLayout = 'table';
// This JS file checks the form for required fields and correct syntax:
print '<scr' . 'ipt src="/x/plugin/plugin.js.php?' . htmlspecialchars($_SERVER['QUERY_STRING']) . '" type="text/javascript"></scr' . 'ipt>';
</script>
<style type="text/css">
html {
height: 100%;
width: 100%;
background: #FFFFFF; /* Old browsers */
font-family:'微软雅黑','宋体',Arial, Helvetica, sans-serif;
}
body {
height: 100%;
width: 100%;
margin: 0;
border: 0;
background-position: center center;
-webkit-background-size: cover;
-o-background-size: cover;
-moz-background-size: cover;
background-size: cover;
font-size:12px;
font-family:'微软雅黑','宋体',Arial, Helvetica, sans-serif;
color:#333333;
}
body.box{
background-image: url(images/bg1.jpg);
background-color:#adc8db;
}
#main_bg{
position: absolute;
top: 40%;
left: 50%;
width: 20%;
height:10%;
text-align: left;
background-color: rgba(255, 255, 255, 0.8);
color: #333333;
margin:0 0 0 -176px;
-webkit-box-shadow:0px 1px 2px #7d7d7d;
-moz-box-shadow:0px 1px 2px #7d7d7d;
box-shadow:0px 1px 2px #7d7d7d;
padding:50px;
background-color:#ECEFF1;
}
#logo{
position:absolute;
top: 32%;
left: 50%;
width: 172PX;
height: 43px;
margin:0 0 0 -176px;
}
#headerDiv,#titleDiv,#contentDiv,#footerDiv{
background-color: rgba(255, 255, 255, 0.8);
border:none;}
td input{ width:234px;}
label.req{display:none; width:0px;}
div.explanation{display:none;}
.input input{ background-image:url(/mailings/268/tmpl/438/images/input.jpg);
width:70%;
height:36px;
font-size:14px;
font-family:'微软雅黑','宋体',Arial, Helvetica, sans-serif;
color:#999999;
border:none;
padding-left:10px;}
textarea{ background-color:#25282b; width:222px; height:136px; border:none;}
.buttons button{background-image:url(/mailings/268/tmpl/438/images/aniu1.png);
width:97px;
height:39px;
border:none;}
p.buttons{ text-align:right;}
fieldset.odd, fieldset.even {
padding: 0px;
margin:0px;
text-align:left;}
</style>
</head>
<body class="box">
<div id="logo">
?<img src="images/logo.png" alt="CSS，求见教！" />
</div>
<div id="main_bg">
<div class="editable">
plugin content goes here
<input type=text>
</div>
</div>
</body>
</html>
[解决办法]
用js去控制输入框的样式
[解决办法]
