How to edit Container Background Color Opacity?

[ecksacutioner]

I'm new to CSS and I've found this code on line 139, which I've edited the end of to include opacity:

#wrapper { width: @wrapper_width; margin: 0 auto; overflow-x: hidden; opacity: 0.5;}

The problem is, this takes everything on the forum (text, links, banners, etc.) and applies that opacity level.  I only want the container background color to be opaque.  What is the best way to handle this?  Thanks!

[T.C.]

Try pasting this at the bottom of your StyleSheet.

.container > .content { background-color: rgba(0,0,0,0.1); }