When writing the CSS code for your site, you can make use of CSS Custom Properties (Variables) to speed up the development process. You can use variables to define properties (size, color), which can then be applied to several elements.
That way, it is possible to have more control over the code and the design. Altering the value of a variable in one place overrides the value of that property everywhere it is invoked.
This post will explain how to use CSS Variables and some practical applications.