When adjusting the font size under Settings > Appearance, the font size value that pops up while dragging the handle currently appears below the slider. While that causes no issues on the desktop application, it results in the value being blocked from view by the user’s finger on the mobile version.
I recommend moving it to appear directly above the slider handle or, better yet, in a stationary editable field next to the slider track (affording the added benefit of the user being able to manually enter a specific value if desired).
This was previously posted as a feature request (there are screenshots in the comments and a link to a general complaint about the font size UI):
I don’t see this behavior anymore — the tooltip now appears above the slider. But it can still end up under my finger because the interface itself changes size as you move the slider, which is disorienting.
If possible I think it would be better to use a preview box to show the size change, and only apply the change everywhere when the slider is released. Also to show the font size in a permanent box next to the slider: