CSS functions are a type of CSS value that can be used to represent more complex data or invoke special data processing or calculations.
color-mix() is a new experimental function that takes 2 colors and returns the result by mixing them. Sounded interesting, but it looks like no browsers can easily use it at the moment.
polygon() allows you to create different polygon shapes and patterns. This function is compatible with all browsers.
saturate() allows you to saturate or desaturate an image. All browsers are compatible with this function.
scale3d() transforms and resizes an element in a 3d space, and scales using a vector at the same time compared to scalex(), scaley(), scalez(), and scale(). All browsers are compatible with scale3d().
CSS functions allow you to change elements to your liking, and include many different ways to do so. This includes transforming, math, filters, colors, images, content, fonts, shapes, references, and grids