There was much new code (part of the goal) in 115 that eliminated much of the CSS that many (including myself) have used through the years, although such CSS has never been supported by Thunderbird. Discovering replacement CSS with the new environment will be a matter of individual experimentation. SO, what that means is that some of the CSS tweaks that we have used may not be available in the near future, if at all. CSS is no specialty of mine so I also am waiting to see what new CSS becomes available.

Thanks again David. Some of the CSS coding works and was hoping to find others that may have solved issues with those parts that do not work now (e.g. items in my original question).

Brant, there's an excellent CSS-Thunderbird 115 discussion thread, with all three of your items covered, in the Browsers and Mail sub-forum of the Windows Eleven Forum. If you run through it and read the posts, you'll come away with all three answers.

https://www.elevenforum.com/t/thunderbird-115-css-customization.16320/

Wisewiz, yes good discussion thread, thanks....and did find how to add message grid lines, but do not see any solution on alternating message background color or the pane splitters. Maybe overlooked?

I'll look for it and post a direct link. I think it's called "zebra striping," and the pane splitters are there if you use the more modern Cards view. However, I've got them in the Table view, too, so I'll find that for you. Back soon.

I posted zebra striping several times in past few days, so if you search form for zebra, those should pop right up.

Thank you, David. I couldn't find it over there on ElevenForum, but now I know I saw it HERE, from you.

Brant, the link for David's zebra post is https://support.mozilla.org/en-US/questions/1418491

And, as for line dividers in the table view: https://www.elevenforum.com/t/thunderbird-115-css-customization.16320/post-319273

See my shot below for the evidence. Click to enlarge.

David: Thanks for zebra striping, works well. Wisewiz, thanks for message divders, also works well. The only thing I cannot find is the pane splitter commands but now think I like the looks of layout without the extra width for the dividers that go between panels.....Thanks both!

Brant. You might come by and mark your query solved. David's solution did it.

Hey! Free beer all around. :)

Now there’s a suggestion I can get enthusiastic about!

General question - is it possible for Tbird 115 to not read a css file at all - 100% - even if the userChrome.css file is located in the right profile? Toolkit legacy etc is set to true? Thanks.

I have yet to encounter a situation where it didn't work, but I've encountered several situations where there were errors in the setup. However, on the question, I guess it's possible. What I have found are misspellings of the css file, css file in wrong profile, css in wrong folder in profile, css with errors.

Thanks David. I've checked all these and am sure that are all correct. This might be the cause of this weirdness. I am having the issue on a used Dell e7470 laptop I bought on eBay. There are three user names - default, public and Dell User. I have tried various methods to change the Dell User name to one I use a lot - dvdsom - using netplwiz. It shows as my updated user name in netplwiz but when I look at users under file explorer still shows as Dell User. I am placing the css file under the Dell User profile as dvdsom is not there. Is there some foolproof way to do this user name change in registry or somewhere - if any chance this is the problem?

My suggestion is to just follow the active profile and leave the use id alone. click help>troubleshootinginformation, scroll down to profile folder, click 'open profile' and then look at the chrome folder (chrome, not Chrome) folder to verify that your userChrome.css file is there. Are you seeing all file suffixes? (I ask that because some people create userChrome.css.txt and, not seeing suffixes, don't realize the file is wrongly named.)

Thanks.

@dvdsom23:

There is a way to actually change the user name in File Explorer > users, but it's complicated and error-prone.

https://www.elevenforum.com/t/change-name-of-user-profile-folder-in-windows-11.2133/

I think you should follow David's advice and stick with what you've got, unless obsessive-compulsive behavior is getting the best of you, and you just MUST change that Dell User to dvdsom. In that case, follow the tutorial in the link carefully and precisely, and you'll get your dvdsom in the users folder.