If you are going to give us an update that breaks our Custom Linux Themes (in my case Linux Mint 20.1 Cinnamon Edition) then why not give us the option to customize all the colors in Thunderbird so we can pick an area and change its colour to what we want?? The latest update to Thunderbird Supernova has left my custom purple theme for linux dysfunctional in Thunderbird (which it has worked ever since I made the theme). Now all I have is dark grey parts all over the place and I can't change it!! Updates are supposed to be improvements not break existing things that worked perfectly for years!! Now I am stuck with this half broken dark grey ugly theme and I am looking at replacement email programs because it is so disgusting!! It was like all fine yesterday!!