Master Page With Content Page

 Master Page

<div style="width:100%;margin-left:-15px;margin-top:80px">
    <div style="margin:auto;width:1000px">
    <table width="100%" align="center">
    <tr>
     <td width="15%"></td>
    <td width="85%">
 <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
       
    </asp:ContentPlaceHolder>
</td>
</tr>
</table>
</div>
</div>

Content Page

<table width="100%" style="border:1px solid gray">

<tr valign="top" >
<td width="100%">
<table width="100%">
<tr valign="top">
<td  class="Details" width="100%" colspan="2">

Contents

</td>
</tr>
</table>
</td>
</tr>
</table>