How is this done?

Check out the page below. Half way down the page there are related youtube videos. When you hover over one of them, the title and description are shown. How is the hover effect achieved? Is it CSS, javascript, etc..?

http://www.realhs.com/apple-yeah-about-that-palm-pre-itunes-sync-feature%E2%80%A6/

 

Yes, it's CSS. Cool eh?

 

i think that's a javascript using jQuery

 

i pulled the page apart. it is both CSS & JS. didn't strip down the CSS or JS yet. thanks.