Add more Agora dialogs styling

* Move more size/margin/padding related styles from generals styles to
  Apex.
* Make dialog content in Agora scrollable.
* Add Agora-specific icons.

Bug: 65504
Change-Id: I17b80b8cf8953d774f0e47bab640d7160d26cfd0
Merge "Add more Agora dialogs styling"