User interface themes
The interface theme defines the appearance of windows, dialogs, buttons, and all visual elements of the user interface. By default, PyCharm uses the Darcula theme, unless you changed it during the first run.
Change the UI theme
In the Settings/Preferences dialog Ctrl+Alt+S, select Appearance & Behavior | Appearance.
Select the UI theme from the Theme list:
IntelliJ Light: Traditional light theme for IntelliJ-based IDEs
macOS Light or Windows 10 Light: OS-specific light theme available as a bundled plugin
Darcula: Default dark theme
High contrast: Theme designed for users with color vision deficiency
It is also possible to create your own UI themes for PyCharm and customize the built-in themes. For more information, see IntelliJ Platform SDK Documentation.
You can assign a shortcut to the Theme action, so that you can quickly switch between themes.