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The VCL style infrastructure is very powerful. In the case of TWinControl descendants, you can even define specific hooks for your components using TStyleHook. TStyleHook is a class that handles messages for controls acting as a wrapper for the hooked control. If you have a custom control that you want to be style enabled, inherit from TStyleHook and provide custom processing for that control. For examples, see TEditStyleHook and TComboBoxStyleHook. You need to register the style hook class with the style engine using the RegisterStyleHook method, as shown in the following code:

TCustomStyleEngine.RegisterStyleHook(TCustomEdit, TEditStyleHook); 

Moreover, the StyleServices function returns an instance of TCustomStyleServices, which provides a lot of customization methods related to VCL styles. Check out the related documentation at http://docwiki.embarcadero.com/Libraries/en/Vcl.Themes.TCustomStyleServices_Methods to see all the possibilities.