Custom UI Themes
Beginning with the 2019.1 release, custom UI Themes are supported. Custom UI Themes give designers control of the appearance of built-in UI elements. The UI Themes available for download illustrate the creative possibilities.
Creating a new UI element for a plugin is distinctly different than Custom UI Themes.
This section discusses creating and customizing UI Themes:
For plugin developers, Exposing Theme Metadata discusses the format of customization keys and information how to provide it to Theme authors.