Two types of customization are available
Simple customization of existing themes. This lets you change colors and images, and some fixed site content. It does not support actualy alterations to the themes. No technical knowledge is needed.
Advanced customization. You have access to the raw CSS, HTML, JS and php code used by the CMS. This is not for the faint of heart, and not for people who don't know what I'm talking about. The WebTeam can set you up with a sandbox site if you want to go here. You can even create your own theme. For something minor, the WebTeam will likely volunteer to do it.
