Main Navigation "Active" state color add

I have been working with your wonderful Theme and have a few challenges that I have not been able to overcome in regards to customizing it. I am fairly familiar with CSS and have been trying to find the correct place to add an “active” state color to the main navigation item. I was wondering if this was possible as I have tried at least 10 different piece to no joy.

I am also having a weird glitch on the side bar widgets that only occurs on one page of the site.

The site is paulchristomd.com

Thanks for your help