Improve layouting so that different screen sizes get a consistent user experience

[jonas-pietzsch]

Currently the left sidebar navigation has a fixed width. The content area on the right side will occupy the rest of the window width. Problem: on smaller devices, screens with low resolution or devices on which accessibility helper tools are used so a very high zoom factor is used, the content part becomes very small (if not even invisible).

Solution: Use automatic layouting using native power of CSS, e.g. flexbox or native CSS grid layout.