Hey Jordan,
first thing: shame on me. I found the colour-option to change the colour of the lines – and so I got rid of them.

1. BUT: one line is still there, that I want to eleminate, too. The very thin one between the Sidebar and the Main Content.

2. Even worse: I can’t change anything within the Sidebar. I can’t change the ratio between Sidebar and Main Content for example – it just doesn’t do anything. Furthermore I’d like to center the text of the Menu and can’t figure out how to. There are just options for left and right, but even they don’t work – the Menu Text sticks to the left all the time.

3. And one more thing: I uploaded two fonts. The Font Nexa Bold should diplay my Menu Items in the Sidebar. This works in Edge, but doesn’t work in Chrome. I’ve deleted my Chrome cache, tried it in Incognito Mode – neither has worked. Edge is always fine. In Chrome the font Roboto is displayed.

Something really strange seems to be going on. and before I invest more of my sleeptime into debugging, I’ll let the experts do the work. In the private content you find the login to my site.

Hey there! Thank you, but I nailed it.
Finally I found this 2015 support post from Yigit that has solved the problem.
https://kriesi.at/support/topic/codeblock-in-fullwidth-how-to/
Can be closed here.

Thank you Victoria, but its hard to believe, that there is no workaround for this problem. Isnt there a way to get a codebox or textbox to full screen view?