By now most developers use CSS custom properties on the regular, but few understand them deeply enough to harness their full power. Lea will take you on a journey from the practical to the mind-blowing, and from the widely implemented to the cutting edge, demonstrating a host of tips, tricks, and gotchas relating to CSS variables in her trademark interactive style. You will leave this talk with both your CSS toolbox and your mind refreshed, and a much deeper understanding of CSS custom properties that you ever thought possible.