(see guidelines for overcoming access barriers)
Take time to move through this website. The links in the left-hand side navigation behave like tabs so that the text of the section heading of the area the user is in becomes darker to show what section the user is in.
This is achieved by setting the hover, active and focus settings of links in CSS. Be sure to remember the a:focus or keyboard users will not get the same experience as mouse users.
Also ensure your link styles are placed in the right order in your CSS. This should be a:link, a:visited, a:hover, a:focus, a:active. More information on link style order.