Sidebar Help

Hello, I have the latest version of wordpress and I’m using the Kubrick design. What I’m trying to do is change the colors from gray to white on the ‘Sidebar’ widget titles; like Pages, Categories, Archives, etc. Also where it says ‘Posted’ I do not like the concept that it is gray. If anyone can help me change these Widgets from gray to white, it would help me out so much. My site is almost done and its the last thing I need to finish it. Thank you.
https://travsthum.com