Primer is built on systems that form the foundation of our styles, and inform the way we write and organize our CSS. Building upon systems helps us make styles consistent and interoperable with each other, and assists us with visual hierarchy and vertical rhythm.
We use Sass variables to keep color, typography, spacing, and other foundations of our system consistent. Occasionally we use Sass mixins to apply multiple CSS properties, they are a convenient solution for frequently-used verbose patterns.
We've documented variables, mixins, and the systems they are built on for the following: