WP-Codebox uses some CSS elements that are widely used by many themes. This makes installation a bit of a pain since it will overwrite your CSS settings.
So far, I found that the following conflicts with my theme:
body { ... }
a { ... }
a:hover { ... }
.left { ... }
.right { ... }
You definitely should not overwrite the theme's body, a, and a:hover, but .left and .right is not as bad to define in codebox.css.