Userpanel interface is designed to allow its easy adoption to your own needs and to blend into your existing web pages layout. There is no need to modify templates code to achieve this goal.
All important files, that is css styles definition and images are located in style directory, each style in separate directory, corresponding to its name. If any of the files is missing, the one from the default style will be used instead. Styles directory, besides css, images and Javascript, contains two simple Smarty templates, one containing global page layout with main menu and content of chosen module below (body.html) and one with table layout, used by modules to draw anything inside the box (box.html).
Each of Userpanel modules can be styled too, as it contains corresponding style directory within its directory structure. If any of the file is missing in specific style, the one from main style directory will be used instead.