An interview question that tests a good mix of HTML, CSS3, JavaScript.
Note there are two routes people can go down -- one is to use the animate() function in jQuery but the route I opted for uses CSS3 transitions/animations.
If people opt for the animate() route, be sure to let them know about this route as that will lead into creating unique id's or using promises to fill the next progress bars. This can still be elegant and you should be open to accepting that as a possible solution, but it makes a lot more sense to keep view related code in CSS and HTML if possible.