谷歌浏览器中外联css样式id失效

asp.net 项目中我引用外联css样式，当我第一次用class时样式没问题，当我把class改为id后样式失效，再改为class时样式也失效，把class换个名称样式又没问题了，但是id肯定有问题，大神们这到底是啥问题啊浏览器谷歌 css asp.net id --------------------编程问答--------------------

代码呢不然没办法看问题。看ID是不是原来声明过了？用chrome F12开发工具瞅瞅！ --------------------编程问答-------------------- /* CSS Document */
body
{
    background-position: left -20px;
    margin: 0px;
    background-image: url('../images/body_background.png');
    background-repeat: repeat-x;
    width: 100%;
    height: 100%;
}

#headerv
{
    width: 100px;
    height: 40px;
}

.header1
{
    width: 100px;
    height: 40px;
}

<%@ Master Language="C#" AutoEventWireup="true" CodeFile="masterpage.master.cs" Inherits="masterpage" %>

<!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 runat="server">
    <title></title>
    <link href="css/MasterPage.css" type="text/css" rel="Stylesheet" />
    <asp:ContentPlaceHolder id="head" runat="server">
    </asp:ContentPlaceHolder>
</head>
<body>
    <form id="form1" runat="server">

    <div id="headerv">后台管理</div>
    dfsdf
    <div>
        <asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">

        </asp:ContentPlaceHolder>
    </div>
    </form>
</body>
</html>
--------------------编程问答-------------------- 谷歌浏览器中样式在matched css rules里面压根就没出现 --------------------编程问答-------------------- 除

补充：.NET技术 ,  ASP.NET

谷歌浏览器中 外联css样式id失效

谷歌浏览器中外联css样式id失效