Bootstrap Resources General Bootstrap CSS Bootstrap Components boostrap-sass Bootstrap Helpers Grid System The Subtle Magic Behind Why the Bootstrap 3 Grid Works Bootstrap: Advanced Grid Tricks - You really should be defining your own classes (Will Schenk) Customising List of Bootstrap Less Variables A Sass With Bootstrap Workflow (Pivotal Labs) Using Mixins Using Bootstrap as a Mixin Library (Adam Wathan) Twitter Bootstrap's Undocumented Mixins - A Reference for Bootstrap 3