The easiest way would be to use Radzen's Theme Editor (a paid feature). Otherwise you need to build the theme from the provided SCSS files as you are currently doing.
Is there any documentation how granular/deep the themes can be modified using Radzen's Theme Editor. E.g. visual apperance of (any?) Radzen blazor component?
Thank you very much, Korchev. It worked perfectly at first shot, but now I don't know how to use a modified theme (modified copy of one of the existing themes), in my own project, since it has wrong relative paths...