When a SoftMaker Office app launches, the window initially has a dark gray border, common to most native Windows applications. However, once the window has fully loaded, the top border blends into the styled title bar but the side and bottom borders turn whitish and look out of place. I found that while I click and drag to move the window, the side and bottom borders switch to the application's theme color, which looks correct. Once I release the window, the borders revert and become whitish again. Furthermore, I found that there also seems to be anti-aliasing applied to a moving window's title bar (the rounded corners are smooth), but a stationary window has jagged corners.
See the screenshots below comparing a stationary native window (explorer.exe) with a moving SoftMaker Office window and a stationary SoftMaker Office window.
Anyway, thank you to the SoftMaker team for an excellent office suite.