Style Web visual lists to look more native on mobile

[robintown]

We intend to use the Compound Web VisualList component on mobile for Element Call. Slight platform-dependent tweaks to the styles would help make the lists look more native:

• On iOS, the list should have a corner radius of 26px, a 2px gap between items, and items should have enough padding to make them each 4px taller.
• No changes necessary for Android.

iOS designs