There are built in classes, namely:
.padding-xs { padding: .25em; }
.padding-sm { padding: .5em; }
.padding-md { padding: 1em; }
.padding-lg { padding: 1.5em; }
.padding-xl { padding: 3em; }
.padding-x-xs { padding: .25em 0; }
.padding-x-sm { padding: .5em 0; }
.padding-x-md { padding: 1em 0; }
.padding-x-lg { padding: 1.5em 0; }
.padding-x-xl { padding: 3em 0; }
.padding-y-xs { padding: 0 .25em; }
.padding-y-sm { padding: 0 .5em; }
.padding-y-md { padding: 0 1em; }
.padding-y-lg { padding: 0 1.5em; }
.padding-y-xl { padding: 0 3em; }
.padding-top-xs { padding-top: .25em; }
.padding-top-sm { padding-top: .5em; }
.padding-top-md { padding-top: 1em; }
.padding-top-lg { padding-top: 1.5em; }
.padding-top-xl { padding-top: 3em; }
.padding-right-xs { padding-right: .25em; }
.padding-right-sm { padding-right: .5em; }
.padding-right-md { padding-right: 1em; }
.padding-right-lg { padding-right: 1.5em; }
.padding-right-xl { padding-right: 3em; }
.padding-bottom-xs { padding-bottom: .25em; }
.padding-bottom-sm { padding-bottom: .5em; }
.padding-bottom-md { padding-bottom: 1em; }
.padding-bottom-lg { padding-bottom: 1.5em; }
.padding-bottom-xl { padding-bottom: 3em; }
.padding-left-xs { padding-left: .25em; }
.padding-left-sm { padding-left: .5em; }
.padding-left-md { padding-left: 1em; }
.padding-left-lg { padding-left: 1.5em; }
.padding-left-xl { padding-left: 3em; }
.margin-xs { margin: .25em; }
.margin-sm { margin: .5em; }
.margin-md { margin: 1em; }
.margin-lg { margin: 1.5em; }
.margin-xl { margin: 3em; }
.margin-x-xs { margin: .25em 0; }
.margin-x-sm { margin: .5em 0; }
.margin-x-md { margin: 1em 0; }
.margin-x-lg { margin: 1.5em 0; }
.margin-x-xl { margin: 3em 0; }
.margin-y-xs { margin: 0 .25em; }
.margin-y-sm { margin: 0 .5em; }
.margin-y-md { margin: 0 1em; }
.margin-y-lg { margin: 0 1.5em; }
.margin-y-xl { margin: 0 3em; }
.margin-top-xs { margin-top: .25em; }
.margin-top-sm { margin-top: .5em; }
.margin-top-md { margin-top: 1em; }
.margin-top-lg { margin-top: 1.5em; }
.margin-top-xl { margin-top: 3em; }
.margin-right-xs { margin-right: .25em; }
.margin-right-sm { margin-right: .5em; }
.margin-right-md { margin-right: 1em; }
.margin-right-lg { margin-right: 1.5em; }
.margin-right-xl { margin-right: 3em; }
.margin-bottom-xs { margin-bottom: .25em; }
.margin-bottom-sm { margin-bottom: .5em; }
.margin-bottom-md { margin-bottom: 1em; }
.margin-bottom-lg { margin-bottom: 1.5em; }
.margin-bottom-xl { margin-bottom: 3em; }
.margin-left-xs { margin-left: .25em; }
.margin-left-sm { margin-left: .5em; }
.margin-left-md { margin-left: 1em; }
.margin-left-lg { margin-left: 1.5em; }
.margin-left-xl { margin-left: 3em; }
Bootstrap 4 has a new notation for margin and padding classes. Refer to Bootstrap 4.0 Documentation – Spacing.
From the documentation:
Notation
Spacing utilities that apply to all breakpoints, from xs to xl, have
no breakpoint abbreviation in them. This is because those classes are
applied from min-width: 0 and up, and thus are not bound by a media
query. The remaining breakpoints, however, do include a breakpoint
abbreviation.
The classes are named using the format {property}{sides}-{size} for xs
and {property}{sides}-{breakpoint}-{size} for sm, md, lg, and xl.
Examples
.mt-0 { margin-top: 0 !important; }
.p-3 { padding: $spacer !important; }