The spacing scale is a base-8 scale. We chose a base-8 scale because eight is a highly composable number (it can be divided and multiplied many times and result in whole numbers), yet allows spacing dense enough for GitHub's UI. The scale's exception is that it begins at 4px to allow smaller padding and margin for denser parts of the site, from there on it steps up consistently in equal values of 8px.
These variables are encouraged to be used within components and custom CSS. The spacing scale is also used for margin and padding utilities.
Ems are used for spacing within components such as buttons and form elements. We stick to common fractions for em values (and powers of 2 where possible) so that , in combination with typography and line-height, the total height lands on sensible numbers.
We aim for whole numbers, however, GitHub's body font-size is 14px which is difficult to work with, so we sometimes can't achieve a whole number. Less desirable values are highlighted in red below.
Y Padding (em)
Total height at 14px
Total height at 16px
The variables listed above are preferred for use within components and custom CSS. To calculate values with other font-sizes or em values, we suggest using Formula.