Dinosheets 
Dinosheets is a dynamic stylesheet library that provides a Sass / SCSS like experience with rule definitions and mutations. The library is speedy and integrates well with libraries that have run loops (like Ember).
There is a single method for inserting, updating, and deleting CSS rules called css. When the rules should by applied to the stylesheet, calling applyStyles will efficiently update the styles.
Compatibility
Dinosheets tests against older browsers that are harder to get your hands on. Please submit an issue if you'd like another browser added to the matrix.
For compatibility documentation, see quirksmode.