ASPxThemes is a .NET assembly that contains information on all available built-in DevExpress theme source files – with the exception of the Default Theme, which is included in control-related DLLs directly.
The ASPxThemes assembly (the DevExpress.Web.ASPxThemes.v19.2.dll file) can be accessed at the following path: "C:\Program Files (x86)\DevExpress 19.2\Components\Bin\Framework\".
A DevExpress theme consists of the following source files.
Skin files (.skin) store visual settings as control markup. Each theme folder contains a separate skin file for each DevExpress web control (e.g., the ASPxPopupControl.skin file describes visual settings for the ASPxPopupControl).
CSS files (.css) include CSS styles for controls.
Image files (.png, .gif).
DevExpress theme source files are organized in a specific hierarchical structure. All files related to a theme are stored within a corresponding theme folder (see the image below). The theme’s skin files are located at the root of the theme folder. Specific subfolders (such as Web, Editors, etc.) contain images and CSS files that conform to the corresponding control types.
The ASPxThemes assembly is registered within the GAC upon installation. When you use the DevExpress theming mechanism to apply a DevExpress theme, a specific DevExpress ASPxHttpHandlerModule finds the assembly in the GAC, so it is not necessary to reference the assembly or deploy any files to the App_Themes folder. All theme source files are obtained from the assembly automatically.
Set the enableThemesAssembly option to false in the web.config file to disable the use of default themes from the ASPxThemes assembly. This option allows you to avoid overriding your custom theme settings when you provide a custom appearance by modifying the default theme files contained within your project's App_Themes folder without renaming the modified themes.
Since you cannot add a custom theme to the ASPxThemes.dll assembly, you can alternatively create a custom assembly that maintains default DevExpress themes and custom themes. See the Generating a Custom Theme Assembly topic for more information.