Full width test

@3dickulus: This regulare page  is supposed to show full width. 
I created a template-full-width.php template in the child theme and appended the necessary code according to these instructions: 
https://gist.github.com/Netzberufler/792a74d63f24aadcad444f4c9d415c11#file-style-css 

but it still doesn’t spread across the WHOLE browser width (or preferrably 90%)
The content area still seems to be limited. The following picture should show with a max width of up to 2560*1440, but it’s shrinking to the content-container(or whatever that area is called. We need to extend that area)