How to change width in css

The snippet box is set to 602 pixels width and I would like to change it to 520 to eliminate the overlap with my sidebar. I tried inserting the css change into both the plugin stylesheet and my site stylesheet, but it still looks the same. Any idea what I’m doing wrong?

Here is the code I used:

#snippet-box { width: 520px; }

http://www.rockhoundmap.com/the-most-expensive-bathtub-in-the-world/

http://wordpress.org/plugins/all-in-one-schemaorg-rich-snippets/