I'd like to have an option to have a real #000 black font color in site's UI. Gray is not helping my eyes to get better. Oh, and narrow fonts are awful. Don't use them in UI, please.
Is it possible to have bigger fonts?
I'm nearly eighty.
Why don't you simply let the browser zoom? Opera has a slider bottom right, you can also press Control-+ / - on the keyboard
I don't use Opera much any more.
For Vivaldi I am using Chrome.
I've magnified to 150% in Chrome and it is perfect.
You can also force a minimum font size. Go to Chrome's Settings page and click "Show advanced settings.." on the bottom. In the "Web content" section there is a button "Customize fonts…", in the box that pops up is a slider "Minimum font size". Move it to the right to suit your needs