Twenty Fourteen- styling the featured post

Hello!
I am using Twenty Fourteen with a child theme.

All is going well, but we would like to put a pale background or some kind of border around the text of the featured post. I tried targeting “featured-post” in the CSS using background or border commands, but no response…

Anybody have any idea how to change display of just the featured post?
(We want to leave style of all other posts alone).

Thanks for any wisdom!