User interface themes
The interface theme defines the appearance of windows, dialogs, buttons, and all visual elements of the user interface. By default, WebStorm 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.
Alternatively, press Ctrl+` and select Theme from the Switch list.
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
Select Sync with OS to let WebStorm detect the current system settings and use the default dark or light theme accordingly.
You can install a custom theme from the JetBrains Plugin Repository as described in Managing plugins.