User283571144 posted
Hi mozina,
changing background color of asp webpages from master
According to your description, I couldn't understand your requirement clearly.
Do you mean you want to change the background color from master page with css?
If this is your requirement, I suggest you could consider setting body's background-color css style to achieve your requirement.
More details, you could refer to below codes:
Notice: Changing the body's background-color css in the master page will make all the web page's body background-color css is the same color.
Master:
<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="Site1.master.cs" Inherits="AspNetNormalIssue.Site1" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title></title>
<style>
body {
background-color:aqua;
}
</style>
<asp:ContentPlaceHolder ID="head" runat="server">
</asp:ContentPlaceHolder>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</div>
</form>
</body>
</html>
Result:

Best Regards,
Brando