Our goal is to create a system that enables us to build consistent user experiences with ease, yet with enough flexibility to support the broad spectrum of GitHub websites. This goal is embedded in our design and code decisions. Our approach to CSS is influenced by Object Oriented CSS principles, functional CSS, and BEM architecture.
Highly reusable, flexible styles
Styles can be mixed and matched to achieve many different layouts, independent of their location. These styles fall into three categories:
Single purpose, immutable styles, that do one thing well.
Scaffolding for common page and content layouts.
Abstracted patterns for frequently used visual styles.
Systematically designed for GitHub
Primer CSS is built upon systems that form the foundation of our styles such as spacing, typography, and color. This systematic approach helps ensure our styles are consistent and interoperable with each other.
Highly composable spacing scale
The base-8 spacing scale is highly composable and works with the density of GitHub’s content. Margin and padding spacers bring consistency to vertical and horizontal rhythm, while remaining flexible so you can tweak layouts to work for every context.
Font size and line-height options work together to result in more sensible numbers. Font styles come in a range of weights and sizes so that we can style appropriately for content and readability. Type utilities allow us to change the visual styles while keeping markup semantic.
The color system allows us to add meaningful signals to content and interactions. Color variables and utilities offer thematic styling options without being tied to structure. Text and background colors come in a range of accessible combinations to ensure we build inclusive interfaces.
Primer CSS bundles
Each component or group of styles is distributed via npm as a separate CSS file, or “bundle”. We also distribute “meta-packages” for core (shared) elements, product-specific (github.com) styles, and marketing.