A singleton that provides access to static information about [Theme] resources used by the engine and by your project. This singleton provides access to static information about [Theme] resources used by the engine and by your projects. You can fetch the default engine theme, as well as your project configured theme. [ThemeDB] also contains fallback values for theme properties. Returns a reference to the default engine [Theme]. This theme resource is responsible for the out-of-the-box look of [Control] nodes and cannot be overridden. Returns a reference to the custom project [Theme]. This theme resources allows to override the default engine theme for every control node in the project. To set the project theme, see [member ProjectSettings.gui/theme/custom]. The fallback base scale factor of every [Control] node and [Theme] resource. Used when no other value is available to the control. See also [member Theme.default_base_scale]. The fallback font of every [Control] node and [Theme] resource. Used when no other value is available to the control. See also [member Theme.default_font]. The fallback font size of every [Control] node and [Theme] resource. Used when no other value is available to the control. See also [member Theme.default_font_size]. The fallback icon of every [Control] node and [Theme] resource. Used when no other value is available to the control. The fallback stylebox of every [Control] node and [Theme] resource. Used when no other value is available to the control. Emitted when one of the fallback values had been changed. Use it to refresh the look of controls that may rely on the fallback theme items.