{**
 *
 * The classes are named using the format .m{sides}-{size} for xs and {property}{sides}-{breakpoint}-{size} for sm, md, lg, and xl.
 *
 *
 * Where sides is one of:
 *
 *    t - for classes that set margin-top
 *    b - for classes that set margin-bottom
 *    l - for classes that set margin-left
 *    r - for classes that set margin-right
 *    x - for classes that set both *-left and *-right
 *    y - for classes that set both *-top and *-bottom
 *    blank - for classes that set a margin on all 4 sides of the element
 *
 * Where size is one of:
 *
 *    0 - for classes that eliminate the margin or padding by setting it to 0
 *    1 - (by default) for classes that set the margin to $spacer * .25
 *    2 - (by default) for classes that set the margin to $spacer * .5
 *    3 - (by default) for classes that set the margin to $spacer
 *    4 - (by default) for classes that set the margin to $spacer * 1.5
 *    5 - (by default) for classes that set the margin to $spacer * 3
 *    auto - for classes that set the margin to auto
 *
 * $spacer value could be redefine by $spacer variable in variables.scss.
 *
 *}

How it works

Assign responsive-friendly margin or padding values to an element or a subset of its sides with shorthand classes. Includes support for individual properties, all properties, and vertical and horizontal properties. Classes are built from a default Sass map ranging from .25rem to 3rem.

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.

Where property is one of: m - for classes that set margin

Where sides is one of:

Where size is one of:

(You can add more sizes by adding entries to the $spacers Sass map variable.)

Example

Here are some representative examples of these classes:

.mt-0 {
    margin-top: 0 !important;
}
    
.ml-1 {
    margin-left: ($spacer * .25) !important;
}
    
.px-2 {
    margin-left: ($spacer * .5) !important;
    margin-right: ($spacer * .5) !important;
}
    
.p-3 {
    margin: $spacer !important;
}

Horizontal centering

Additionally, Bootstrap also includes an .mx-auto class for horizontally centering fixed-width block level content—that is, content that has display: block and a width set—by setting the horizontal margins to auto.

Centered element
<div class="mx-auto" style="width: 200px;">
    Centered element
</div>
mt-1
my-1
mb-1

ml-1
mx-1
mr-1