This is a simple question I guess

I just want to modify the rectangle displayed around a quoted text block and make it a 1px solid line, without the 3D / shadow effect that is default for vBulletin. I'd like it to look like the attached example.
I already tried to edit the bbcode_quote template but obviously I don't know what to change. So, how do I get a simple 1px white (or any other color of my choice) frame ?
Thanks for your help.