The single responsibility principle applied to CSS — CSS Wizardry—CSS, Web Standards, Typography, and Grids by Harry Roberts.
It is so awesome to see the resurgence in knowledgable contributions to the discussion of CSS. Not just the latest preprocessor or newest CSS3 snippet, but honest-to-goodness foundational concepts of CSS implementation.
CSS is super powerful, and that often goes unnoticed. Between OOCSS, SMACSS, and articles like this, your mind might just melt a little.