This is a nice way of highlighting the menu items a user is hovering over. It expands the current (potential) selection and reduces the sizes of the other items. It is all done with CSS and HTML.
First, let's set up the HTML:
This is simply a title with 3 menu items in an unsorted list.
And the CSS? Not much more to it.
Above is the CSS required to get it working but without particularly beautifying the page layout. The JSFiddle link has a little more formatting in place - it is pretty ugly but that is to highlight how the it works.
Take a look at this JSFiddle for a working example.
Here is a random example of some of our work.