The navigation bar at the top, the fixed footer bar at the bottom, and everything in between is laid out with Bootstrap. I'm also using Bootstrap heavily in the games I programmed.
I've used bootstrap heavily on many projects, including Bootstrap 3, which I'm fond of. AlishaSparkles.com includes a customized Bootstrap, with 2 custom button definitions (btn-alisha and btn-alisha2!) Why? I didn't want to change the btn-primary, as there are a few places we use it in other areas as is.
I can work with the Less or Sass versions, I'm fluent in both.