[Evolution] Changing background color of mail view

[Felix Matouschek <felix matouschek org>]

Hello,

I'm using Evolution on Fedora 35 with the Adwaita-Dark theme and the 
preview of HTML mails is using a black font color on a dark grey 
background, which is really hard to read.

Mails that explicitly set their background color (e.g. to white) are 
displayed correctly. I would like to change the default background color 
of HTML mails to something lighter. Is that still possible with 
~/.config/gtk-3.0/gtk.css?

I found this [1] on Launchpad, but that does not work for me. Which 
selectors need to be specified to change the default background color of 
HTML mails? Which selectors need to be specified to change the 
properties of plain-text mails?

Thank you,
Felix

[1] https://answers.launchpad.net/ubuntu/+source/evolution/+question/195187