• Complete MDN CSS Reference (don't learn this by heart!): https://developer.mozilla.org/en-US/docs/Web/CSS/Reference
• Are you a reading guy? Find written CSS docs on MDN: https://developer.mozilla.org/en-US/docs/Web/CSS
• Common CSS Properties Reference: https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Properties_Reference
• CSS Combinators: https://developer.mozilla.org/en-US/docs/Learn/CSS/Introduction_to_CSS/Combinators_and_multiple_selectors
• More details on CSS Specifity: https://developer.mozilla.org/en-US/docs/Web/CSS/Specificity