Off topic, but it is really uncomfortable to read anything on medium because 25% of my screen is covered by header containing 'Sign In' and 'Get Started' and by footer with 'Get Updates' button.
In addition to the solutions in the sibling comments, let me offer my favorite one: a simple bookmarklet that zaps all sticky elements on the page. Works wonders in Medium and a lot of other sites.
I usually just drop into the browser dev tools and delete those elements. But I also try to avoid medium, blocking its domains by default and only unblocking if I really, really want to read something (which is becoming increasingly uncommon, since I don't like how medium basically say "we need to share your data with third parties"). I blocked medium in my hosts file for a while, but that turned out to be a little bit too inconvenient. I usually hope that the HN comments can give me enough information so I can stay away from medium...
I only recently realised that tapping the “stacked horizontal lines” icon to the left of the url in iPhone safari enables a reading view which removes this stuff.