Improve styles of h2 elements in articles

This commit makes the visual hierarchy of the page a little clearer by
removing the bottom border from h2 elements in articles and making them
a little smaller than the title of the article.

Change-Id: Ifba0ec699d933efe352ad568800802ae7a3a1952
Reviewed-on: https://gerrit.causes.com/23660
Tested-by: Joe Lencioni <joe.lencioni@causes.com>
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Lann Martin <lann@causes.com>