keynav rectangle is black and fuzzy on the insides on Xubuntu 20.04

[bgoodr]

Hi,

I'm trying to use keynav built from sources.  Does anybody have any idea as to why I'm seeing this in keynav? (see image below). The image was taken using my cell phone because the key grab prevents taking a screenshot.

This is running under Xubuntu 20.04 on Linux.

I've played around with various changes to the source code, but I cannot see how to fix it. The youtube videos, that demo keynav on Linux that I've seen, do not show that black interior, with fuzzy edges. What might be the cause of this?

Thanks!