3 levels deep. If you find yourself going further, think about reorganizing your rules (either the specificity needed, or the layout of the nesting). – Github CSS Styleguide
to stay DRY ȗ use @imports to improve file organization ȗ concat & minify ȗ nesting: Rule of 3 ȗ use normalize/reset.css ȗ global.css for global styles ȗ simplicity : KISS