Twitter Bootstrap: margin-bottom built in css class

Now available in bootstrap 4

Example-

<div class="mb-5 p-5"> margin-bottom and padding with size 5 </div>

You can use-

m for margin
p for padding

And for sides:

t - top
b - bottom
l - left
r - right
x - both left & right
y - both top & bottom
blank -all sides

For size- 0,1,2,3,4,5

There is no bootstrap class for margins like you describe. The reasons would be the need for classes for margins 0 to 10s or 100s, as well as the need for multiple units, such as px, em, %, etc.

You can make your own classes fairly easy. Even easier with sublime text-editor and multi-select.

That being said, you don't want to abstract every style rule into the html. Original CSS is useful for something particular to your element, such as margins. Using bootstrap classes for every style would lead to difficult to read HTML.

This Question is tagged Bootstrap 3, but when you update to Bootstrap 4, there is a built in utility for this.

Boostrap 4 has a spacing feature that solves that problem https://getbootstrap.com/docs/4.0/utilities/spacing/

But, in you are sticked to older bootstrap version or can't use it a all and in case you need a complete list of margin and padding classes, here it is

/* MARGINS & PADDINGS */
.p-xxs {
  padding: 5px !important;
}
.p-xs {
  padding: 10px !important;
}
.p-sm {
  padding: 15px !important;
}
.p-m {
  padding: 20px !important;
}
.p-md {
  padding: 25px !important;
}
.p-lg {
  padding: 30px !important;
}
.p-xl {
  padding: 40px !important;
}
.m-xxs {
  margin: 2px 4px;
}
.m-xs {
  margin: 5px;
}
.m-sm {
  margin: 10px;
}
.m {
  margin: 15px;
}
.m-md {
  margin: 20px;
}
.m-lg {
  margin: 30px;
}
.m-xl {
  margin: 50px;
}
.m-n {
  margin: 0 !important;
}
.m-l-none {
  margin-left: 0;
}
.m-l-xs {
  margin-left: 5px;
}
.m-l-sm {
  margin-left: 10px;
}
.m-l {
  margin-left: 15px;
}
.m-l-md {
  margin-left: 20px;
}
.m-l-lg {
  margin-left: 30px;
}
.m-l-xl {
  margin-left: 40px;
}
.m-l-n-xxs {
  margin-left: -1px;
}
.m-l-n-xs {
  margin-left: -5px;
}
.m-l-n-sm {
  margin-left: -10px;
}
.m-l-n {
  margin-left: -15px;
}
.m-l-n-md {
  margin-left: -20px;
}
.m-l-n-lg {
  margin-left: -30px;
}
.m-l-n-xl {
  margin-left: -40px;
}
.m-t-none {
  margin-top: 0;
}
.m-t-xxs {
  margin-top: 1px;
}
.m-t-xs {
  margin-top: 5px;
}
.m-t-sm {
  margin-top: 10px;
}
.m-t {
  margin-top: 15px;
}
.m-t-md {
  margin-top: 20px;
}
.m-t-lg {
  margin-top: 30px;
}
.m-t-xl {
  margin-top: 40px;
}
.m-t-xxl {
  margin-top: 50px;
}
.m-t-xxxl {
  margin-top: 60px;
}
.m-t-n-xxs {
  margin-top: -1px;
}
.m-t-n-xs {
  margin-top: -5px;
}
.m-t-n-sm {
  margin-top: -10px;
}
.m-t-n {
  margin-top: -15px;
}
.m-t-n-md {
  margin-top: -20px;
}
.m-t-n-lg {
  margin-top: -30px;
}
.m-t-n-xl {
  margin-top: -40px;
}
.m-r-none {
  margin-right: 0;
}
.m-r-xxs {
  margin-right: 1px;
}
.m-r-xs {
  margin-right: 5px;
}
.m-r-sm {
  margin-right: 10px;
}
.m-r {
  margin-right: 15px;
}
.m-r-md {
  margin-right: 20px;
}
.m-r-lg {
  margin-right: 30px;
}
.m-r-xl {
  margin-right: 40px;
}
.m-r-n-xxs {
  margin-right: -1px;
}
.m-r-n-xs {
  margin-right: -5px;
}
.m-r-n-sm {
  margin-right: -10px;
}
.m-r-n {
  margin-right: -15px;
}
.m-r-n-md {
  margin-right: -20px;
}
.m-r-n-lg {
  margin-right: -30px;
}
.m-r-n-xl {
  margin-right: -40px;
}
.m-b-none {
  margin-bottom: 0;
}
.m-b-xxs {
  margin-bottom: 1px;
}
.m-b-xs {
  margin-bottom: 5px;
}
.m-b-sm {
  margin-bottom: 10px;
}
.m-b {
  margin-bottom: 15px;
}
.m-b-md {
  margin-bottom: 20px;
}
.m-b-lg {
  margin-bottom: 30px;
}
.m-b-xl {
  margin-bottom: 40px;
}
.m-b-n-xxs {
  margin-bottom: -1px;
}
.m-b-n-xs {
  margin-bottom: -5px;
}
.m-b-n-sm {
  margin-bottom: -10px;
}
.m-b-n {
  margin-bottom: -15px;
}
.m-b-n-md {
  margin-bottom: -20px;
}
.m-b-n-lg {
  margin-bottom: -30px;
}
.m-b-n-xl {
  margin-bottom: -40px;
}
.space-15 {
  margin: 15px 0;
}
.space-20 {
  margin: 20px 0;
}
.space-25 {
  margin: 25px 0;
}
.space-30 {
  margin: 30px 0;
}

It's taken from Homer Responsive Admin Theme by WebAppLayers. I guess author don't mind sharing that. It probably will save 20min of time of some Web Developer out there.