Bug 1082908 - Background color of contact list should be other than white so that it differ from empty space

no, we need to target the specific list; that's `#messages-recipient-suggestions .contact-list` or `#messages-recipient-suggestions ul`. Please find similar rules in the CSS so that you group them together.

Bonus if you add a class to this contact-list (for ex: `recipient-suggestions-list`) and use the class instead, but I won't block for this.