CSS/HTML我怎樣不重疊固定報頭

有像頭一個Twitter /臉譜，固定一個和主內容。當我滾動到我的最後一行時，內容div與標題重疊。我怎樣才能避免這種情況？CSS/HTML我怎樣不重疊固定報頭

這是我的網頁截圖： enter image description here

這是我的HTML結構：

<body> 

<div> 
<?php include("initcontrols/header.php"); echo $plHeader;?> 
</div> 


<div id="mainform"> 
<noscript>It seems your browser doesn't support Javascript.<br /></noscript> 

<!-- Apply blue theme as default for all tiles --> 
<div id="tiles" class="blue"> 
<!-- Sliding Tile that shows 100% of the back tile every 3 seconds --> 
<div class="live-tile" data-stops="100%" data-speed="750" data-delay="3000"> 
    <span class="tile-title">slide tile (figure 2a)</span> 
    <div><img src="images/say.jpg" width="180" height="180" alt="1" /></div> 
    <div><img src="images/sayako.jpg" width="180" height="180" alt="2" /></div> 
</div> 

    <!-- Red Flip Tile that flips every 4 seconds --> 
<div class="red live-tile" data-mode="flip" data-delay="4000"> 
    <div> 
     <img src="images/home.png" alt="3" /> 
     <a class="tile-title">flip tile front (figure 2b)</a> 
    </div> 
    <div> 
     <img src="images/message.png" alt="4" /> 
     <a class="tile-title">flip tile back (figure 2b)</a> 
     </div> 
</div> 


<script type="text/javascript"> 
// apply regular slide universally unless .exclude class is applied 
// NOTE: The default options for each liveTile are being pulled from the 'data-' attributes 
$(".live-tile, .flip-list").not(".exclude").liveTile(); 
</script> 

</div>

我的CSS：

div#header{ 
padding-left:15px; 
overflow:hidden; 
position: fixed; 
margin:0px; 
top:0px; 
left:0px; 
display: block; 
width: 100%; 
height: 90px; 
-moz-box-shadow: 0 1px 2px rgba(0, 0, 0, 0.5); 
background:#333333; 
background: -moz-linear-gradient(center top , #736F6E, #111111) repeat scroll 0 0 transparent; 
} 
div#header-title{ 
color: #FFF; 
float: left; 
display:inline-block; 
} 
div#header h2{ 
margin: 0 0 0 3px; 
z-index:12; 
} 
div#header h1{ 
margin-top:0; 
margin-bottom:0; 
} 

#mainform{ 
width:960px; 
background: #F0F0F0; 
border: 1px solid #CCC; 
height: 2000px; 
margin: 100px auto; 

}

和我活瓷磚外觀： http://pastebin.com/cpBXYVRu 我通過http://www.drewgreenwell.com/projects/metrojs#applicationBar使用的模板：

來源

2012-12-10 bEtTy Barnes

有這種https://developer.mozilla.org/en-US/docs/CSS/z-index – ManseUK

的讀取嘗試建立一個JS提琴。這會有很大的幫助。 –

它有PHP嗎？ @MichaelGiovanniPumo你知道 –