Hi Leo,
I tried deleting the cache, but no help. In fact, when I leave Customizer after saving the changes and then come back, the font size for widget content is saved (e.g. in my case 14 px), but the front-end of the website shows the regular 17px font size. I think it has to do something with the fact that I am using a child theme. When I switch to the orignal theme, things seem to be working fine. I used Childify Me plugin to create the child theme.
Have you noticed issues with child themes? I mean, I can live together with the original theme as I only plan to make some CSS changes which I can put directly in the Customizer – but still, over time I might need to do some other changes and then it would be useful to use the child theme.
Thanks!
Vladimir