Currently there are many bugs with the default html and css layouts, specifically on mobile. Things like nav bar clipping/sticking, components having internal scrolling, dual vertical scrollbars, horizontal scrollbars (ie the default width of the app is always larger than the screen).
These can easily be seen in the example apps such as online shop, and here is a basic example of an app with just a card component and a column panel with all default settings where on mobile you will get horizontal scroll bars. Anvil | Login
-Please advise