The Rebalance Theme by Automattic is a new 3 column theme. You can check the Rebalance theme demo here. Previously I shared Rowling theme Modifications which is a 2 column site. But I showed how to make it 3 columns too ( in the Rowling theme’s comments section).
Here I have shared the Rebalance theme modifications using which you give your Rebalance theme a new look.
You can use my shared code and ask question in the comments section.