I've got my editor toolbar laid out the way I want, but would just like to get rid of the huge border around the preview button - which doesn't occur on the site here, I notice, I guess because of the way the icons are placed on the right side.
I'm not sure, to be honest, but thanks. My initial fix above, of just moving a couple of icons over to the right didn't actually work out too well, since there was still a sizeable border around the preview button (about half what it was), but I got everything laid out mostly the way I wanted by doing a button configuration reset and keeping to a similar icon placement in terms of the rows. So this:
Got me this:
Which is good enough. It's definitely all a little janky, though. For example, after I did the above layout, I just had to go experiment and see what would happen if I simply moved the two icons on the third row to the end of the second row, and once again I ended up with that long preview border, and putting them back on the third row where they originally were didn't get rid of it. I had to do another reset and do it all over again. So I'm not messing with it any more.