The concept for the progress bar is shamelessly stolen from Twitter's
bootstrap styling system.
The background is a
repeating-linear-gradient, with a
fallback to a solid colour. A
background-size is set
to above 100%, so that the gradient doesn't have a veritcal cut-off
that may show up when it is animated.
The animation is CSS
animation of the
background-position-x, which does involve a little bit
The amount of bar that is filled is set by changing the
right value on the inner div. You can also do RTL
bars by the same method.