border: 10px solid red;

Using [https://support.mozilla.org/en-US/questions/1544905 https://support.mozilla.org/en-US/questions/1544905] as an example I placed this in my profile's userchrome.css and restarted thunderbird: .calendar-month-day-box-current-month[relation="today"] { border: 10px solid red; } It seems not to be working in thunderbird 148.0.1 (64-bit on windows 11). So I found the today panel in the debugger and added '''border: 10px solid red;''' to its element. That worked perfectly, as the attached image confirms. It also confirms the class is correct and that it contains the today relation. I can't see the userchrome.css file in the debugger, which seems strange. But I edited the body colour in userchrome.css and that worked, so I know the file is being used. So why is the change to the today panel being ignored? To confirm that I had the correct userchrom