Edit: As @Bauke pointed out, apparently this feature already exists via tapping outside of the sidebar. I never even thought to try that.

I'm not sure if this is in the gitlab issues or not, but a cursory search suggested it's not. On mobile, if you tap the link to the most recent comment from the sidebar, you navigate directly to that comment just as on the desktop site, but the sidebar remains open and can't be closed without scrolling all the way back up to the top of the page. This is incredibly cumbersome and inconvenient.

Ideally there would either be a method of closing the sidebar from anywhere, or for the sidebar to close on clicking the link. I would imagine that the latter would be simplest.

I noticed that Tildes docs make a point out of using words instead of labels. The stated reason is that icons may be difficult to understand, and I honestly don't get how is this the case.

Icons, when used right, are much more usable and intuitive than any text labels. They are small, distinct, they draw attention and you can tell what they do just by looking at them instead of reading them.

Take the classic upvote/downvote scrollers used on Reddit, Imgur, etc. It uses icons for upvotes and downvotes, but there isn't a single person I know who doesn't know what those mean. It's intuitive and usable. It doesn't require localization. It just works.

In contrast, the "Vote (10)" button on Tildes. It uses text, on a page full of text. It's an important UI element, one of the most used UI elements really, but it's not visually highlighted in any way. The amount of votes, which is an important metric, isn't distinct, making it hard to read. The "text button" style it uses is usually reserved for buttons that are used rarely, such as "Edit" or "Delete", or buttons that open more menus, such as "Edit" or "Reply". It's not intuitive.

Yes, this is a minor thing, but it's minor things that make the overall experience pleasant or unpleasant. And it shows how icons (and highlights), when used right, make user experience better.