User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36

Steps to reproduce:

• Start Thunderbird
• Create a new calendar event with any name and any date, e.g. now plus 2 minutes
• Wait until the for the calendar event time has come

Actual results:

• The calendar reminder popup pops up.
• The field "Details" is almost unreadable, because it color is similar to the blue color of the popup. See attached file.

Expected results:

• "Details" should be readable like in the previous versions of Thunderbird. This behavior has changed a few days ago.
• I did not change any coloring in the settings. The new behavior appeared suddenly without any color changes from my side.