CSS already has plenty of useful functions, like calc() , min() , max() , and clamp() . They let you build more flexible styles without repeating the same logic. CSS custom functions let you take this idea a little further. The @function at-rule lets you define your own functions, pass them values, and return a result that you can use in your styles. Syntax Before we build anything, let's quickly look at the basic syntax: @function --function-name ( --par...