width auto in bootstrap 4 code example

Example 1: how to make hr class bootstrap full width

/* It is done with the <hr> tag. Then you need to give it a class name, and adjust the margin accordingly. See below for an example. 
  */

.solid {
  margin: 0 -15px;
  border: 0;
  border-top: 1px solid #c9c7c7;
}

Example 2: bootstrap height and width sizes

<div style="height: 100px; background-color: rgba(255,0,0,0.1);">
  <div class="mh-100" style="width: 100px; height: 200px; background-color: rgba(0,0,255,0.1);">Max-height 100%</div>
</div>