eBook NAV with CSS - help!

I'm eager to learn how to create a variant of the often-discussed drop down menues using CSS.

I have seen many examples of "ready to use" NAV solutions, but not one describing how to go about to make one like this:

http://egyptiska.se/

The thing I'm so impressed with is that the "drop-down" actually drops down INSIDE the NAV.
And that it also includes a pointer along the side of the NAV showing which option is hoovered above.

Any suggestion or links to where I can find out how to create this effect?

Thanks,
jaxz