The platform includes two ready to use themes: Halo and Havana. By default, the application will use the one specified in the cuba.web.theme application property. The user may select the other theme in the standard Help > Settings screen. If you want to disable the option of selecting themes, register the settings screen in the web-screens.xml file of your project and set the changeThemeEnabled = false parameter for it:
link:../../../../../../source/gui/themes/themes_1.xml[role=include]