GTK+ was giving me a few issues with large black borders around some windows, I created a CSS file to modify this to remove the box shadow around the window and the border.
There is still a tiny but annoying black around the window where there is a border radius and I have been trying to eliminate that.
After debugging for a little while I figured out its due to the fact that it cannot display transparency correctly and just displays black instead.
Here is an example:
Is there any way of doing this with the gtk's implementation css alone?