Replace mentions of Mayo theme in User Guide

Yeah, I suppose we could use Olivero for now. But it doesn't have a stable release and the project is marked as not under Security team. Plus we would have to change it again later when Olivero becomes part of Core, and I don't think Bartik would be removed then.

I don't think that creating a new theme with Classy as the base would be difficult to do. It would need to be a contrib project with a stable Drupal 8/9 release, in order to be a drop-in replacement for the topics about downloading themes from drupal.org. And in order for the tests/screenshots to work, we need to make 2 releases so that we can download the older release and verify that it shows up on the Available Updates page for that topic.

We could call it Market and use the farmer's market color scheme, perhaps with a slight variation from the color module settings that we set up in the User Guide using Bartik so you can see when you install it that the site look changes.

We could base on Classy for now though. If Classy goes away in 10.x (should not happen before then), which is 2 years from now, we could update the theme then.

Actually it looks like the right thing to do is to use stable9 as the base theme. See this change record:
https://www.drupal.org/node/3107179

I would have suggested Stark, except:
#2854576: Discourage use of Stark as a base theme (and possibly mark it internal or hidden)

Right. But I think stable9 would be available at least until the end of Drupal 10, so we would have 4 years to rely on it and somewhere in there we could switch the base to stable10 and probably the theme would still be OK because we would only have added a bit of CSS. Maybe we would need a small tweak but probably not much.

Since one of the example farms in the User Guide scenario sells honey, and the name was not in use, I just created the Honey theme project on drupal.org:
https://www.drupal.org/project/honey

The Git repo is currently empty. I am now going to go ahead and create the actual theme, and see how minimal I can be. My thought is to make it mobile-friendly and use the Color module, with the User Guide farmer's market colors as the defaults.

If anyone would like to co-maintain the theme with me, let me know either on this issue or in the Honey project issue queue.

OK, I've made a workable, if very ugly theme. See also #3154671: Make this theme less ugly.

The next task on this issue would be to update the User Guide to download this theme instead of Mayo.

I also need to go back to #3147242: Drupal 9 compatibility for User Guide tests and see about making new screenshots that use this new theme instead of Mayo. I don't think there's a screenshot in the User Guide of the site with Mayo turned on, so I don't think we'll need to wait on the theme being made less ugly... although it does need a thumbnail graphic.

The Honey theme now is much less ugly, and has a 1.0.0 release! We need to update the User Guide to use it as an example instead of Mayo.

Updated issue summary with this task.

When we do this, we will need to get new screenshots to replace the Mayo ones. For each language, the images that need to be replaced are:
extend-theme-install-appearance-page.png
security-update-module-updates.png
security-update-theme-updates.png

Other changes to 9.1.x not related to the Mayo theme should go on #3176742: 9.1.x compatibility for User Guide, thanks!

As I'm not sure what you mean by the "maintenance page", I haven't added comment #16 to that issue. So if you could add a comment to the other issue and explain which URL within a site, and/or which User Guide topics, and/or which User Guide screenshots you think are affected, that would be super helpful, thanks!

Here's a patch for the User Guide English source text. The Mayo theme was only mentioned in one file.

Screenshots will also need to be updated:
- I'm running the User Guide Tests project now (which makes automated screenshots). Those screenshots will be done sometime soon.
- There's also one non-automated screenshot of drupal.org, but the image is generic enough that I don't think it needs to be updated (extend-theme-install-download.png).

Screenshots were committed on #3176742: 9.1.x compatibility for User Guide, so I will mark this as RTBC based on previous comment.

Committed! Sending out email shortly.