I have created a custom theme with the Theme Builder but I have notice that many, if not all, of the URL references in the css files contain server-side code blocks. Since I am adding links to these files directly the server side code does not get executed.
Example from the SearchBox css file:
.RadSearchBox_BP_FormDefault .rsbLoadingIcon {
background-image: url('<%=WebResource("Telerik.Web.UI.Skins.BP_FormDefault.Common.loading_small.gif")%>');
}
The example linked in several of the existing threads does not provide any information.
http://docs.telerik.com/devtools/aspnet-ajax/controls/grid/appearance-and-styling/modifying-existing-skins#creating-a-custom-skin-basic-steps