Thank you so much. All of your suggestions worked.
Have a nice day!
Thank you for the answer. I’ve found the bug. It was close to where you pointed me. The issue was the padding in Customizing > Header > General.
The bottom padding was not defined, and that caused the problem. Apparently Safari had no problems with that, but other browsers showed a white stroke instead. Now I’ve set it to 1 px, and it works for all browsers.
Thanks for the help!
Thanks for the tip! Unfortunately it didn’t get better with all plugins disabled expect for Ocean extra. So it seems like the plugins are not causing the problem I guess. If you have any other suggestions I would love to hear them.