Expanding or Shrinking an area in website like Youtube

As an user Youtube is a great video sharing service .As a web developer ,Youtube like any web 2.0 service ,comes with many effects . One of them is changing the size of video are ,expanding or shrinking with a click . when you click on "wide" button ,video area expand to a larger size ,sidebar goes down and content in video area stretch fully . When you click on 'normal' ,video area shrink to