Attaching a Custom Theme Assembly
To apply a theme from a custom theme assembly created with the ASPxThemeBuilder tool, you will need to reference the assembly within your project.
In the Solution Explorer window, right click the site's References folder and click Add Reference...
Click the Browse... button, select the required theme assembly, and click Add.
This adds the assembly to the project's References folder. Set this assembly's Copy Local property value to true - to copy this assembly to the web server when deploying.
Assign the assembly name to the customThemeAssemblies option in the devExpress web.config section.
<devExpress> <themes customThemeAssemblies="MyThemeAssembly" ... /> ... </devExpress>
You can now apply the custom theme to your project .
A custom theme assembly's version (major and minor versions) should match other DevExpress assemblies used within the project. If the version is different, upgrade the theme assembly's source code, rebuild the assembly, and upgrade corresponding references in the target MVC application. See the following KB Article for more information: KA18887: KA18887: How to update custom themes after upgrading a project to a new version using ASPxThemeBuilder.