title: What is the meaning of $spacer in bootstrap?
body: <p>I am new to bootstrap. I came aloing this documentation on bootstrap:</p>
  <pre><code>https://getbootstrap.com/docs/4.3/utilities/spacing/
  </code></pre>
  <p>Here is writed that when we write for example mt-1 that means:</p>
  <pre><code>1 - (by default) for classes that set the margin or padding to $spacer * .25
  </code></pre>
  <p>what means in this situation $spacer * .25 ?</p>