Bug 1030972 - Import tasks from Bugzilla

@bobsilverberg @Osmose r?
Yes, it can definitely be accomplished another way. `content-container` lightens the background of the element it's applied to and adds a margin. I'm using it to make the "Are you sure?" prompt stand out, as in the wireframes. I can make another class especially for that purpose, but I thought reusing `content-container` would be good. Any idea why `content-container` might be best used only once? Is anything else relying on that assumption?