Hello Matjaz Cof,
As you have already seen we are providing styling to some of the standard controls provided my Microsoft. As custom controls may greatly vary it is virtually impossible for us to provide styles and themes for your custom controls.
As for making your control look like ours I would suggest look at the XAML of each control / control part and extract from there whatever necessary to make your controls look the same way. You can find the XAMLs for all themes in your telerik installation in the Themes folder.
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