Yes, all browsers work fine now, including Opera. It was a one-time glitch that I got out of by killing and restarting Opera. I was just wondering what I could possibly have done to cause it.

I think distraction-free writing is the answer. Ctrl-Shift-F. The classic editor doesn't seem to have the button for it. The image on the linked WordPress page portrays the block editor, which I don't use. But I think Ctrl-Shift-F gives me what I saw before - in Opera, and also in Firefox and probably Chrome too.

So it wasn't an Opera issue after all. In which case I am doubly grateful for your efforts. I'm saving a note on it for future reference. Thank you and take care.

There should be a ready option to disable tab islands. At present, doing so is complicated and disruptive.

First, to close an existing island, I had to click on a tab within an island, and then mouse over the vertical bar at the left edge of the island. That opened up an option to Close Island (2 tabs). Moving the mouse very carefully, after a half-dozen tries, I was finally able to get the mouse cursor to reach that option before it vanished. But then I discovered that clicking that option would close my tabs as well as the island. I had to manually copy their URLs and create separate tabs to reopen those webpages. Closing the copied tabs then closed the island.

To disable creation of future tab islands, I went to opera://settings/?search=islands. That gave me an option to turn off "Automatically create tab islands."

Yes, all browsers work fine now, including Opera. It was a one-time glitch that I got out of by killing and restarting Opera. I was just wondering what I could possibly have done to cause it.

I think distraction-free writing is the answer. Ctrl-Shift-F. The classic editor doesn't seem to have the button for it. The image on the linked WordPress page portrays the block editor, which I don't use. But I think Ctrl-Shift-F gives me what I saw before - in Opera, and also in Firefox and probably Chrome too.

So it wasn't an Opera issue after all. In which case I am doubly grateful for your efforts. I'm saving a note on it for future reference. Thank you and take care.

Thanks for the improvement in post title. I've never had the problem before, in any browser, so I guess I just assumed it was an Opera-specific issue. But yes, you are correct in figuring out that this relates to the WordPress classic editor.

At this point, the only person in this exchange competing with me for the title of Chief Dummy is the guy who told me I should have searched for solutions before posting.

So, as I said at the start, the problem relates to the header, and also to what I guess we could call the footer.

Normally, when editing in WordPress, I see the header (shown above) above the editing box (where I type the text of the post I am composing) and also a footer area, below the editing box, where WordPress offers additional options (e.g., add tags, save draft, publish).

Somehow, the header and footer suddenly disappeared, and I was left with the editing box. I couldn't tell if there was merely blank space above or below that box, because unfortunately I had enlarged the box to fill the screen.

Phrasing it differently, the rightmost vertical scrollbar was gone. Normally that would enable me to move up (above the editing box) or down (below the editing box). I was left with only the scrollbar inside the editing box.

So, to repeat, something happened while I was editing in WordPress, and the effect of that "something" was that I was left with only the editing box, and no apparent way to see what (if anything) might lie above or below.

One might guess that I had inadvertently stumbled upon some hotkey that caused all this. But I have disabled hotkeys in Opera precisely to prevent this sort of thing.

It's OK if you don't know and want to treat this as a mystery (which it does seem to be) or possibly a WordPress issue. I tried asking WordPress for an assist, but I wound up in an endless chat circle with an expert who could not understand what I was saying. I know you'll want to chalk that up to incoherence redux on my part, and that's OK too, even though it wasn't.

Present status, then: a mystery. Thanks, anyway, for trying to help. Take care.

Yes, thanks, and you're welcome to read that article several times, if you'd like.

It's really just what I described. Normally, when I'm working in the editor, I see the header, or whatever it's called - the part shown in the image, with the post's title, URL, Add Media button, etc. Also, normally I see the part at the bottom - the footer, if you will - where I can add Tags, click Publish, etc.

For some reason, those header and footer spaces disappeared, or at least I was unable to access them. I would say it must have been because I had hit some magical hotkey, but I don't believe it has ever happened before - and anyway, this was in Opera, where I've disabled hotkeys.

I could only see and work in the text editing box itself. That was fine, as far as it went - I was able to continue working - but there was no way to save or do anything else. I ultimately just had to kill the browser, restart, and rely on autosave to recover what I'd been writing.

@leocg Sorry, not sure I understand. Are you suggesting that you cannot name a portion of the screen until I have read through all that material?

What is the name of this part of the editor, and its opposite number on the bottom end? I tried searching for Opera header and footer, but that wasn't it.

And now that I know the correct terminology, why would this Whatzit disappear, and how could I get it back?

I was left with only the editing space; and since I have disabled hotkeys, my recourse was to pull the plug and have faith in the autosave.

I think I found a solution. In the left-sidebar menu, click WPAdmin. It opens a new tab with the desired icon.

Here's the situation:
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The left sidebar shows the desired tab icon (i.e., a black-and-blue Microsoft Windows icon). The tab itself just shows the default WordPress icon. Until a recent system change, the tab was displaying the desired icon. Now it doesn't. How can I persuade Opera to display that icon?

I saw somewhere that I might be able to restore the desired icon by clicking on the heart icon at the right end of the address bar. Clicking on that does display the default WordPress icon, but I don't see any way to direct it to the folder where I have stored a copy of the desired icon.

Oh. I do, now that you mention it. It's a search icon. It didn't occur to me that it would search tabs. I guess I must have assumed that it was for, like, Google search.

Alright. Micro-mystery solved. Thank you!

@leocg Thanks for the quick reply. The new button is what I'm talking about -- it's not there. I don't have a button that shows the list of opened tabs.