You can override the css per template

You can override the css per template

I have done that manually, as I said in the original post, but it means going back and forth from inspecting Cassiopeia layout and copying CSS, adding it to the new template CSS and then checking it in the new layout. A bit of a pain. There is a JCE template override for the pop-up, but that's no use if not using JCE.

Rather than using admin CSS, could the tinymce have its own CSS in the templates > system folder?
Or perhaps its own template override?

You can use this: https://wysiwyg.dgrammatiko.dev

It will give you way better results, actual WYSIWYG, from the core or any other 3rd PD editor

Oops. I've just found the Joomla > Layouts > Tinymce but all it does is create an empty folder. I shall add a CSS file and test it now.

It would be more useful if it included the CSS in the override.

Do you want to style tinyMCE or the content inside the editor?

Joomla > Layouts > Tinymce

That is not for css!!

See https://www.youtube.com/watch?v=OyZQ63Ahnt4&ab_channel=LearnJoomla4

tinyMCE's own layout. This is because my template didn't include 'modal' CSS as I don't use modals anywhere, so the initial view is like this:

Joomla > Layouts > Tinymce

That is not for css!!

See https://www.youtube.com/watch?v=OyZQ63Ahnt4&ab_channel=LearnJoomla4

Yes, I watched that yesterday and saw it's for text snippets and templates, but thought it might work for CSS, too.

so the initial view is like this:

Where's the editor in that view?

Go to http://skin.tiny.cloud/t5 and create a custom skin
Then place it in your template CSS folder (IIRC)

Go to http://skin.tiny.cloud/t5 and create a custom skin Then place it in your template CSS folder (IIRC)

Thank you @dgrammatiko - I'll give that a try.

NO!!!

You're talking at cross purposes

This is NOTHING to do with tinymce!!

This is not tinymce layout!!!

Your issue is to do with the styling of the modals for the xtd-editor plugins - to confirm that just disable all the xtd-editor plugins and they will disappear

Ok. ok. Perhaps the xtd-editor modals plugins CSS could be added to System CSS then?

You can style the XTD by adding CSS to the layouts/joomla/editors/buttons/button.php and layouts/joomla/editors/buttons/modals.php.

This is because my template didn't include 'modal' CSS as I don't use modals anywhere, so the initial view is like this:

If you are using frontend editing and the xtd-editor plugins then you ARE using modals

You can style the XTD by adding CSS to the layouts/joomla/editors/buttons/button.php and layouts/joomla/editors/buttons/modals.php.

In my custom template:
How do I insert a css file in the head tag of the iframe?
I put in the modal.php file:

$doc = JFactory::getDocument();
$doc->addStyleSheet(JURI::base( true ).'/templates/joomla-italia-theme/css/system-j4.min.css');

not work