I'm currently working on OrganicCSS - a micro framework based on atomic CSS concept. I'm thinking a lot for name conventions, classes and of course mixins. I decided to combine three mixins in a file called _box-model.scss. They will provide a shortcuts for margin, padding and border properties.

If you plan to make an animation by using position: absolute and set top, left, right or bottom please don't. Just use translate. It's just better, as Paul Irish proves.