How to: Disable ASP.NET Themes
You can configure a page or control to ignore themes. Themes override local settings for page and control appearance by default. Disabling this behavior is useful when a control or page already has a predefined look that you do not want the theme to override.
You can give precedence to control settings on the current page by applying a theme as a style sheet theme. In that case, the theme is used to set properties that have no local settings, but explicit local settings take precedence. For details, see.
To disable themes for a page
Set the EnableTheming attribute of thedirective to false, as in this example:
<%@ Page EnableTheming="false" %>
To disable themes for a control
Set the EnableTheming property of the control to false, as in this example:
<asp:Calendar id="Calendar1" runat="server" EnableTheming="false" />