With the dokuwiki template, the preview on mobile devices is pretty much unusable as has a margin/border equivalent to the width of the sidebar in order to simulate the reduced width because of the sidebar. This border should be hidden when the content takes 100% of the width anyway (on small screens). I'm aware that the editing experience hasn't been optimized for mobile devices yet but in my experience at least with Chrome apart from the preview it works quite well.
A possible fix is
https://github.com/splitbrain/dokuwiki/pull/499