Merge pull request #11812 from edx/PERF-276

common/static/sass/bourbon/css3/_animation.scss

common/static/sass/bourbon/css3/_backface-visibility.scss

common/static/sass/bourbon/css3/_background.scss

common/static/sass/bourbon/css3/_box-sizing.scss

common/static/sass/bourbon/css3/_perspective.scss

common/static/sass/bourbon/css3/_radial-gradient.scss

common/static/sass/bourbon/css3/_transform.scss

common/static/sass/bourbon/css3/_transition.scss

common/static/sass/bourbon/css3/_user-select.scss