Unfortunately there is no comprehensive guide or tutorial on this subject yet. Shortly, styles (themes) are described by https://nitisa.com/reference/core/interfaces/IStyle interface. It stores all the style settings which should be used to replace standard layout properties of widgets you want to change. Instance of the style can be assigned to entire form by its setStyle() method or to any control (widget with visual representation) using the same method. You can see how style is created in Nitisa/Core/DefaultStyle.h and corresponding Nitisa/Core/DefaultStyle.cpp files. Most widgets have private method called UpdateFromStyle(). You can check these methods to see what properties may be changes via style. For example, check file Packages/Standard/Controls/Button/Button.cpp, line ~1187. We will add a guide about this subject as soon as we get a chance.