For one of the sites I maintain, I was tasked with doing, as the client called it 'A new front page and make it more mobile friendly'. Well, there's no super simple way to do that easily without hacking a lot of a not-so-responsive Drupal theme. So, I pitched the idea for a complete re-theme, got them to agree, and started learning more frontend skills.
In the process, I've picked up some more JQuery (don't forget to check for document.ready), and a WHOLE lot of SASS.
For some reason, I was having a bit of a time tracking down exactly what Bootstrap's SASS variables were for their breakpoints / screen sizes, so I'm just documenting them here, both for my future reference, and yours.