PS - one day, and that day may never come...
Opera will allow users to vary the width of the scroll bar; my eyesight and dexterity are not those of a 18-year old...

Indeed, but I can see no purpose to having a 'minimum' width, especially when in cases such as mine, it is not nearly narrow enough - you'll note that the 'maximumum' is way over there:
far closer to the right-hand side of the screen than the minimum to the left. It strikes me as illogical and arbitrary. And annoying...

Thanks for your help.

@vux777 Yes, my monitor is 1920x1080, and all the settings (display and Oracle) are at 100%, (as usual). I don't know how to measure the width of the sidebar, but it's still too wide...!

....wait! I can see some of the issue; I use a separate monitor with my laptop, so side by side they look like this, with the laptop monitor on the right:

It would be fine if I used the laptop monitor, but certainly not on the larger external one. I used to be able to narrow it down to a comfortable width, but no longer, apparently.

@vux777 Many thanks for replying. Yes, that's with both pinned and unpinned.Screenshot attached; I would usually have a sidebar about half of the width of that one shown. This is far too much, and intrudes on the main screen to the extent that newspaper columns are squashed; together with the inevitable adverts, the actual content becomes about half of my screen area.

Astonishingly annoying; (width of favourites sidebar). I thought this issue was dealt with previously, and I was happy, but an unwanted update got past me and now the thing occupies far more of my screen than I want or need.

What's the answer?

Excellent, that worked; many thanks. Why do they spring this sort of stupidity on their users? Highly unprofitable.

@linknetrvh My apologies, I thought I was directing my bile and anger at the people who 'upgraded' the piece of software without my knowledge or consent; my remarks above are what happens when the supplier of a product changes - and not in a good way - the actions of the product on what seems to be a whim.
Again, apologies.

@linknetrvh: Could you step this to a solution, please?

I've no idea what you sods have done, but My screen is very definitely not the way I want it, nor the way I left it last night.