Can you post a before/after screenshot?

Apologies for the delay, here's some screenshots. Note that the original TkAgg draws a white rubber band for the zoom, which is barely visible on a white background, so I've highlighted where it crosses the data

Ah, I assume the problem here is that with a dark theme, the default color is light? I do see a dashed line on my machine with a light themed UI.

Both CI failures are fixed on main, I rebase just to be sure (having now force pushed, I think I could have also closed and reopneed ....).

I rebased and pushed a fix for the webagg backend. On main, we used to get a solid rubberband:

and on this PR previously, we would get a dashed one with the wrong size:

Now with the latest change, we get a dashed one with both black and white, drawn the same way as Qt:

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout v3.10.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 ac6730773bc0b860e8c715f772928453efd7c42f

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #30560: Consistent zoom boxes'

4. Push to a named branch:

git push YOURFORK v3.10.x:auto-backport-of-pr-30560-on-v3.10.x

5. Create a PR against branch v3.10.x, I would have named this PR:

"Backport PR #30560 on branch v3.10.x (Consistent zoom boxes)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

AFAICT, this was not backported, and there's probably no need right now.