>编辑：我仍然没有找到解决方案，但是我已经设法完全避免了这个问题。如果有人知道为什么这不起作用，那将非常有帮助，所以我知道未来。谢谢
-
我似乎无法让它工作，我尝试到处寻找答案。
这是它的要点(全部嵌套在一个模态弹出面板中。
<div class="body">
<div>
<div class="left">
<asp:Label runat="server" Text="Name:" />
</div>
<div class="right">
<asp:TextBox runat="server" ID="txtName" Text="" />
</div>
</div>
另外，我应该补充一点，我可以毫无问题地向正文类添加样式。
我已经在 CSS 中尝试过这些：
.modalPopup .body.left {}
.modalPopup .body .left {}
.modalPopup .body > left {}
.modalPopUp .body > .left {}
正确的班级也是如此。
我错过了一些非常明显的东西吗？
如果需要，我可以给你更多的代码/信息，随时问。
提前谢谢你。
编辑：
这是所有代码
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="smsBatchUI.Default" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajaxToolKit" %>
<!DOCTYPE html>
<link href="modalpopup.css" rel="stylesheet" />
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.1.1.min.js"></script>
<title></title>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<div>
<asp:Button ID="Button2" Text="Pop Up" runat="server" style="display:none" />
<ajaxToolKit:ModalPopupExtender TargetControlID="Button2" ID="mp1" runat="server" PopupControlID="Panel1"
CancelControlID="ButtonCancel" BackgroundCssClass="modalBackground">
</ajaxToolKit:ModalPopupExtender>
<asp:Panel ID="Panel1" runat="server" style="display:normal" align="center" CssClass="modalPopup">
<div class="header">
<header>
Batch SMS Messaging
</header>
</div>
<div class="body">
<asp:CheckBox ID="chkVerify" runat="server" style="display:none" Checked="false" AutoPostBack="true" /><br />
<div>
<div class="left">
<asp:Label runat="server" Text="Name:" />
</div>
<div class="right">
<asp:TextBox runat="server" ID="txtName" Text="" />
</div>
</div>
<div>
<div class="left">
<asp:Label runat="server" Text="Number:" />
</div>
<div class="right">
<asp:TextBox runat="server" ID="txtNo" />
</div>
</div>
<div>
<div class="left">
<asp:Label runat="server" Text="Message: " />
</div>
<div class="right">
<asp:TextBox runat="server" ID="txtMessage" />
</div>
</div>
<div>
<div class="left">
<asp:Label runat="server" Text="Template: " />
</div>
<div class="right">
<asp:DropDownList runat="server" Width="200px" ID="ddlTemplate">
<asp:ListItem Text="Select Template" Value="DefaultValue"></asp:ListItem>
<asp:ListItem Text="HR" Value="HR"></asp:ListItem>
<asp:ListItem Text="CT" Value="CT"></asp:ListItem>
<asp:ListItem Text="IT" Value="IT"></asp:ListItem>
</asp:DropDownList>
</div>
</div>
<div>
<div class="left">
<asp:Label runat="server" Text="Send Date: " />
</div>
<div class="right">
<asp:TextBox runat="server" ID="txtDate" Text="YYYY-MM-DD" /><asp:Label runat="server" Text="(YYYY-MM-DD)" Font-Size="10px" />
</div>
</div>
<asp:Label runat="server" Text="Preview" style="padding-top: 0px" />
<br />
<asp:TextBox runat="server" Height="150px" Width="300px" ID="txtPreview" Text="Click Preview to see your message before you Submit it." TextMode="MultiLine" /> <br />
</div>
<div class="footer">
<asp:Button runat="server" Text="Preview" ID="btnPreview" OnClientClick="Preview();" />
<asp:Button runat="server" Text="Submit" ID="btnSubmit" OnClick="btnSubmit_Click" OnClientClick="Validate()" /> <br />
<asp:FileUpload ID="FileUpload1" runat="server" />
<asp:Button ID="Button1" runat="server" Text="Upload" OnClick="btnUpload_Click" /> <br /> <br />
<asp:Button ID="ButtonCancel" runat="server" Text="Close" />
</div>
</asp:Panel>
</div>
</form>
</body>
</html>
和 CSS：
body { color: #373d3f; }
.modalBackground
{
background-color: floralwhite;
filter: alpha(opacity=60);
opacity: 0.6;
}
.modalPopup
{
background-color: #E8ECED;
width: 400px;
border:1px solid #666666;
border-radius: 12px;
padding:0
}
.modalPopup .header
{
background-color: #014B96;
height: 30px;
color: White;
line-height: 30px;
text-align: center;
font-weight: bold;
border-top-left-radius: 8px;
border-top-right-radius: 8px;
font-family: Helvetica, Arial;
}
.modalPopup .body
{
min-height: 50px;
line-height: 30px;
text-align: center;
font-weight: bold;
padding-left: 10px;
padding-right: 10px;
font-family: Helvetica, Arial;
display: inline-block;
}
.modalPopup > .body > .left
{
width: 30%;
float: left;
text-align: right;
}
.modalPopup > .body >.right
{
width: 65%;
margin-left: 10px;
float:left;
}
.modalPopup .buttonalignleft
{
text-align: left;
}
.modalPopup .footer
{
padding: 6px;
}
我希望这能有所帮助。
*{
margin:0;
padding: 0;
}
p{color:#fff;}
html,body{
width:100%;
height:100%;
}
.modalPopup{
position:relevant;
width:100%;
height:100%;
background-color:#fd3;
}
.modalPopup .body {
position:absolute;
width:90%;
height:90%;
background-color:#f00;
left:5%;
top:5%;
}
.modalPopup .body .left {
width:50%;
height:100%;
background-color:#0f0;
float:left;
}
.modalPopup .body .right {
width:50%;
height:100%;
background-color:#00f;
float:left;}<div class="modalPopup">
<div class="body">
<div class="left">
<p>Left</p>
</div>
<div class="right">
<p>Right</p>
</div>
</div>
</div>