GitHub's developer-platform system: system-font pragmatism at 14px, blue #0969da accents on white canvas (or the famous #0d1117 dark mode), subtle #d0d7de borders around 6px-radius 'Box' containers, semantic success green and danger red, 8px spacing, and functional color tokens (fg.muted, canvas.subtle) shipped as primer/primitives.
Primary actionThe Primer 'Box': content organized into hairline-bordered #d0d7de containers with 6px radii and canvas-subtle #f6f8fa headers — the visual grammar of every repo page, PR, and settings screen on GitHub.