Creating A Gradient Sidebar Border

Hi Flynn, I couldn't find a similar question to this, I apologize if it has been answered already. Basically what I am looking to do is create a gradient on the left border of my left sidebar, and the right border on my right sidebar.

I'm not sure how to accurately explain it, so I will provide an example. If you visit www.thestar.com you will see that the outer parts of the left and right sidebar form a gradual gradient into the outer background.

Any advice on how to achieve this?

Regards,
OZ