Beta 89.0b1 on OSX dark mode not showing properly

Hello, I am on OSX Catalina and recently the interface is behaving strangely on Thunderbird. Not 100% sure, but it seems to be since beta 89.0b1. I attach two screenshots (hope it works) where you can see the problem. One of the screenshots is with the mouse hovering and then one can see the item. I change to the light theme and the problem disappeared. Thanks. Alain