Changing Border Styles for the sidebars

I have version 3.4.9

I am trying to make a "bordless" left side bar (where i will insert an iframe into) and i would like the right to have borders around the widgets so it looks more "bloggish"

I was wondering where does one change the "border options" for the side bars? I know it must be staring me in the face.. If anyone could point me to the right field to edit, that will suffice

I have tried to look through the "add css" section.. but i was confused

thank you in advance