Alright okay thanks for the heads-up! The Skin in question is here:
There are two .wba files in the archive, I used the one with the ° in its name as the other seems even more broken.
Specifically the "Regular Windows" substyle, one change I wish to make there is to add glass to the address-bar area. I managed to do so by cropping some glass-part of the top border and assigning it to the Top Glass Area in SkinStudio but it seems I still have to change something with the side-borders too as there's still a border spilling over as you can see here on the left side for example:
Furthermore when inactive the window-borders are misaligned and my added top glass-area also doesn't fade out like the rest of the frame does.
And then some applications like Logitech G Hub have a weird glass shadow at their right and bottom side, I wonder if that's fixable too.
Thanks for help in advance!