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With Nice Theme API you can add visual styles to your application. Nice Theme resources located in *.ntr files (ntr - nice theme resource) or in *.njr files (njr - nice join theme resource). The .ntr and .njr files are regular dlls, that contains the bitmaps and data for the nice theming engine. Nice theme engine adds join theme resource to the nice theme resource, so you can create your own theme resource for the existing nice theme resource.