I would have different approaches depending on that, One way would be to create a transparent png image and position it on top of your div, another way is using css3 trasparent gradients and ::before or ::after pseudo selectors to place them..
If you’re looking for Modern Browser support, CSS3 can come to your rescue. You can skew a div so that it appears as parallelogram and give opacity accordingly. If you dont want to write too many lines of code animating the ‘keyframes’ in CSS3, you can do that through jquery(positioning it from left to right) by parsing through all the divs. You’ll can to use jQuery animate function.