CSS custom properties
Sit back, listen to Tim explaining and enjoy. This still underused feature is about to make your life a whole lot easier! CSS custom properties, often referred to as CSS variables or cascading variables, are a very powerful feature for building complex apps or websites. It hands you incredible flexibility as well as unlocking interesting possibilities.
Websites are becoming increasingly complex with large amounts of CSS and many values that are repeated in various places. Take, for instance, color themes. If you need to replace a specific color that is used in countless different locations, you’ll have to perform an elaborate search. Custom properties lets you (re)define variables, making it a lot easier to maintain your CSS and achieve cleaner styles.