Custom properties or CSS variables have been available to us for a while now, still it seems they don't get used as much as they should. Custom properties are more than just a constant, they are flexible and smart. In this presentation, I hope to inspire you into using them a lot more often. We'll be styling 4 buttons with less than 20 lines of code, learn to take more control of a grid by using smart variables and add some JavaScript trickery as a finishing touch. Let's optimise our design systems by using custom properties.