bootstrap row with margin code example

Example 1: bootstrap Margin and padding

Use the margin and padding spacing utilities to control how elements and 
components are spaced and sized. Bootstrap 4 includes a five-level scale for
spacing utilities, based on a 1rem value default $spacer variable. Choose
values for all viewports (e.g., .mr-3 for margin-right: 1rem), or pick
responsive variants to target specific viewports (e.g., .mr-md-3 for 
margin-right: 1rem starting at the md breakpoint).

<div class="my-0 bg-warning">Margin Y 0</div>
  <div class="my-1 bg-warning">Margin Y 1</div>
  <div class="my-2 bg-warning">Margin Y 2</div>
  <div class="my-3 bg-warning">Margin Y 3</div>
  <div class="my-4 bg-warning">Margin Y 4</div>
  <div class="my-5 bg-warning">Margin Y 5</div>
  <div class="my-auto bg-warning">Margin Y Auto</div>

Example 2: bootstrap Grid system

The above example creates three equal-width columns on small, medium, large, and extra large devices using our predefined grid classes. Those columns are centered in the page with the parent .container.

Breaking it down, here’s how it works:

Containers provide a means to center and horizontally pad your site’s contents. Use .container for a responsive pixel width or .container-fluid for width: 100% across all viewport and device sizes.
Rows are wrappers for columns. Each column has horizontal padding (called a gutter) for controlling the space between them. This padding is then counteracted on the rows with negative margins. This way, all the content in your columns is visually aligned down the left side.
In a grid layout, content must be placed within columns and only columns may be immediate children of rows.
Thanks to flexbox, grid columns without a specified width will automatically layout as equal width columns. For example, four instances of .col-sm will each automatically be 25% wide from the small breakpoint and up. See the auto-layout columns section for more examples.
Column classes indicate the number of columns you’d like to use out of the possible 12 per row. So, if you want three equal-width columns across, you can use .col-4.
Column widths are set in percentages, so they’re always fluid and sized relative to their parent element.
Columns have horizontal padding to create the gutters between individual columns, however, you can remove the margin from rows and padding from columns with .no-gutters on the .row.
To make the grid responsive, there are five grid breakpoints, one for each responsive breakpoint: all breakpoints (extra small), small, medium, large, and extra large.
Grid breakpoints are based on minimum width media queries, meaning they apply to that one breakpoint and all those above it (e.g., .col-sm-4 applies to small, medium, large, and extra large devices, but not the first xs breakpoint).
You can use predefined grid classes (like .col-4) or Sass mixins for more semantic markup.

<div class="container">
  <div class="row">
    <div class="col-sm">
      One of three columns
    </div>
    <div class="col-sm">
      One of three columns
    </div>
    <div class="col-sm">
      One of three columns
    </div>
  </div>
</div>

Example 3: bootstrap spacing

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
p - for classes that set padding

Where sides is one of:

t - for classes that set margin-top or padding-top
b - for classes that set margin-bottom or padding-bottom
l - for classes that set margin-left or padding-left
r - for classes that set margin-right or padding-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 or padding 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 or padding to $spacer * .25
2 - (by default) for classes that set the margin or padding to $spacer * .5
3 - (by default) for classes that set the margin or padding to $spacer
4 - (by default) for classes that set the margin or padding to $spacer * 1.5
5 - (by default) for classes that set the margin or padding to $spacer * 3
auto - for classes that set the margin to auto

$spacer defaults to 1rem