Need to decide on the box-sizing policy

Some of the dimensions are not consistent on iOS and Android.

Basically the same problem as CSS box-sizing property.

For example when you set `width: 100%`, on Android it actually sets the width to full 100%, which means it will go out of bounds if there's a padding involved, but on iOS the OS makes sure the elements don't go out of bound, so setting `width: 100%` is almost like saying `max-width: 100%`.

Currently a way around this problem is to not use `width: 100%` and rely on autosizing.

But this does need to be addressed and we need to come up with a consistent policy.

No file, test, or entry point is identified in the issue. First clarify the desired box-sizing policy for CSS dimensions across iOS and Android, then document the agreed behavior and guidance for cases such as width: 100% with padding; done means the project has a decided, consistent policy.

Written by the indexing model from the issue text.