1. CSS Relative color syntax

    Relative color syntax in CSS allows a color to be defined relative to another color using the `from` keyword and optionally `calc()` for any of the color values.

  2. types: `<calc-keyword>`

  3. types: `<calc-keyword>`: `e` constant

  4. types: `<calc-keyword>`: `infinity` and `-infinity` constants

  5. types: `<calc-keyword>`: `nan` constant

  6. types: `<calc-keyword>`: `pi` constant