Customization of the user interface can increase the accessibility of company standards and reduce the number of steps required to complete a task.
Most elements of the user interface are stored as part of a customization (CUIx) file and customized using the Customize User Interface (CUI) Editor (CUI command). AutoCAD-based products support two types of CUIx files; full and partial. Full CUIx files contain a majority of the user interface elements that you see in the application window, while a partial CUIx file typically introduces some additional user interface elements that are often associated with your company standards or a specific plug-in. You can load a main CUIx file that defines the standard user interface elements and an enterprise CUIx file that defines the user interface elements based on your company utilities. The Enterprise CUIx file is often a partial CUIx file. The main and enterprise CUIx files can be loaded using the Files tab of the Options dialog box.
CUIx files created from a previous release should work in the latest release without any problems, but any new controls or commands will be missing from the user interface. If you customized the acad.cuix file in a previous release, you should consider migrating your customization using the Migrate Custom Settings utility or the Transfer tab of the Customize User Interface (CUI) Editor instead of using the file in the latest release.
If you have custom partial CUIx files from a previous release, you should be able to copy them to a support search path being used by the latest release and load them using the CUILOAD command.
Starting with AutoCAD 2015-based products, a separate resource DLL file should be created for the light and dark theme if your CUIx file utilizes an external resource DLL for storing custom images. The appropriate resource DLL is used based on which theme is currently applied to the user interface. The naming convention for the DLLs requires you to use the same name as the customization file, but also requires adding the suffix "_light" to the DLL that is to be used for the Light theme. For example, if a CUIx file named mymenu.cuix is loaded, AutoCAD searches for the resource DLL file mymenu_light.dll when the Light theme is current or mymenu.dll when the Dark theme is current.