Consider making the website better suitable on mobile and small screens by implementing media queries

We should spend some time on implementing more media queries into the CSS to make placements work more easily and provide better access to the menu/sidebar.

Feature Branch: tails:web/improve_mobile_layout

Related issues

Related to #13199
Related to #7021 (closed)
Related to #7627

Original created by @u on 13200 (Redmine)

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