How do I use the Spacing Utility Classes in Bootstrap

Question

In this article I saw Bootstrap 4 Spacing Utility Classes, and he uses m-b-lg in className.

<div class="row">     <div class="col-sm-6 m-b-lg">         <!-- column-small-50%, margin-bottom-large -->     </div> </div> 

But when I use it on meteorjs with react nothing happens. Am I missing something or missing a plugin?

<div className="container-fluid">     <div className="col-xs-6 col-xs-offset-3 m-t-lg">         <h1 className="text-xs-center"> Login </h1>         <form>             <div className="form-group">                 <input type="email" className="form-control" id="inputEmail" placeholder="Email"/>             </div>             <div className="form-group">                 <input type="password" className="form-control" id="inputPassword" placeholder="Password"/>                 <p className="text-xs-center"><a href="/signup"> Forgot your email or password?</a></p>             </div>                   <div className="form-group">                 <button className="btn btn-primary btn-block" type="submit"> Login </button>                 <p className="text-xs-center"> New to Arcademy? <a href="/signup"> Sign up now.</a></p>             </div>         </form>     </div> </div> 

Answer 1

Bootstrap 5 beta - update 2021

Now that Bootstrap 5 has RTL support, the concept of left and right have change to start and end. Therefore the *l- and *r- spacing utilities have changed

pl-* = ps-*
pr-* = pe-*
ml-* = ms-*
pr-* = me-*

Bootstrap 4 -update 2020

The Bootstrap 4 spacing utils have changed since the original answer (for v4 alpha). Now the syntax is simply:

• margins: m{sides}-{size}
• padding: p{sides}-{size}

Examples..

mb-2 = margin bottom 2 spacing units
m-0 = no margins
pt-3 = padding top 3 spacing units
p-1 = padding all sides 1 spacing unit

There are now 6 sizes (0-5) that represent a portion of the standard .5rem spacer unit. Additionally, x-axis (left/right) and y-axis (top/bottom) utils have been added:

my-2 = margin top & bottom 2 spacing units
mx-0 = no margins left & right
px-3 = padding left & right 3 spacing units

And, the spacing utils are now responsive. The smallest xs breakpoint is implied when no breakpoint is used.

• margins: m{sides}-{breakpoint}-{size}
• padding: p{sides}-{breakpoint}-{size}

mt-md-2 = margin top 2 spacing units, on md (and up)
py-sm-0 = no padding top & bottom, on sm (and up)

Bootstrap 4 Spacing Utils Demo

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Related: Bootstrap 4 spacing bug?