Github Code Style Overrides

github.css

.tab-size-3, .tab-size-4, .tab-size-5, .tab-size-6, .tab-size-7, .tab-size-8,
.tab-size-9, .tab-size-10, .tab-size-11, .tab-size-12 {
  tab-size: 2 !important;
}

.line-numbers, .file-content.code .line-numbers a, .file-data, .data,
.diff-line-code, .blob-line-num, .blob-line-code, .blob-num, .blob-code,
pre, code {
  font-family: "Hack", "Menlo", "Liberation Mono", "Consolas", "DejaVu Sans Mono", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace !important;
  font-size: 12pt !important;
  tab-size: 2 !important;
}

For Stylish I match domains with the regular expression .*github.*. It even works on gists, and raw view.

This also works for Gitlab.

.*gitlab.*