How to add border to my content?

Hello! I like this theme very much. I built a site with three columns, with main content in the middle. On the left side there'S a news box and a links box. On the right side there's a box with an image slideshow. Now my problem is: How can I put a blue border around each of my boxes? I tried several solutions from this forum, but for my problem they didnt't work..... Thank you very much in advance! Best regards Rumble