Dolphin 7.3.4 System fonts are very small.

Hello
I have Dolphin 7.3.4
Since 2 days the Dolphin system fonts are very small in the backend and frontend.
What can be the problem and where do I find the appropriate CSS
thanks for your help

Sounds more like a browser problem. Chrome and Firefox now allow you to reduce or increase font sizes by a percentage for each site visited. Open your site, then look at your browser settings. You may find the zoom level has been reduced to 80% or less. If not, increase it. I use 125%

Changing all font sizes in Dolphin is complex so I doubt if that's the problem.