two columns, percentage width derived from the column count

second column

three columns with pixel widths (leftover pixels go to the leading columns)

second column

third column

percentage gutter, right-to-left

second column

a single column has no gutter padding at all

four columns: the two inner ones share the same padding rule so upstream merges them into a single comma-separated selector

second column

third column

fourth column

columns in a group keep their desktop padding on mobile

second column