.css file to change calendar background color not working

[J Dodgson]

In T'bird 78 I wrote a userChrome.css file that worked perfectly in determining the colour of the whole cell (not just a small bar at the right-hand edge) in the calendar according to the chosen colour of each category. The .css file was located in the C:\Users\....\AppData\Roaming\Thunderbird\Profiles\......default\Chrome folder.
I am now working with 91.0.3 (64-bit) and it didn't work so I tried to follow some advice in these topics. The code now looks like this:

@namespace html url("http://www.w3.org/1999/xhtml");

.calendar-event-box-container[categories] {margin: 0px !important;background-position: top left !important;background-repeat: no-repeat !important;
}

calendar-category-box[categories]{
display: none !important;
}

/* Adapting background color following category */
.calendar-event-box-container[categories="cfc"] { color: black !important; background-color: rgb(227,149,184) !important;}
.calendar-event-box-container[categories="ldsm"] { color: black !important; background-color: rgb(255,255,102) !important;}

It still doesn't work so obviously I've got something wrong. Is this still the right code, and is it still the right location for the .css file? I notice that since I got 91 I now have a new Profile so I have copied the whole of the Chrome folder and the .css file into the new Profile but with no success.
How can I get the effect I want in T'bird 91?

[morat]

The stack.calendar-event-box-container element doesn't exist in TB 91.

I don't think you can apply the style using a pure css solution.

Reference
http://searchfox.org/comm-esr78/search? ... -container
http://searchfox.org/comm-esr91/search? ... -container

Similar problem: http://forums.mozillazine.org/viewtopic ... #p14903404

Structurally simplify calendar event items
http://bugzilla.mozilla.org/show_bug.cgi?id=1694820

[J Dodgson]

Thank you Morat for this information but it doesn't get me very far does it? If I can't achieve what I want to achieve - and did achieve with TB 78 - using "a pure css solution", how can I achieve it? Is there a non-css solution? There surely must be a solution of soime sort. I have looked at your "similar problem" and I see you offered the same advice. I may be naive to suggest it, but can this problem be pointed out to the developers and they be asked to reinstate what they have removed?
By the way, the second of your two Reference links (the one referring to 91) merely returns the message "No results for current query".

[morat]

You could create an addon like Calendar Tweaks. The addon uses JavaScript to implement some of the tweaks.

Calendar Tweaks (obsolete)
http://addons.thunderbird.net/thunderbird/addon/14384

You may be able to apply the style using the userChromeJS addon.

userChrome.js hack example: http://forums.mozillazine.org/viewtopic ... &t=3079682

Sorry, I don't know a solution offhand.

second of your two Reference links (the one referring to 91) merely returns the message "No results for current query"

In this case, the message "No results for current query" means the calendar-event-box-container class doesn't exist in TB 91.