如何让div增长到包含它的子元素？

<div class="parent clearfix">
  <div class="child"></div>
  <div class="child"></div>
</div>

.clearfix::after {
  content: "";
  display: table;
  clear: both;
}

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
</div>

.parent {
  display: flex;
  flex-wrap: wrap;
}

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
</div>

.parent {
  display: grid;
  grid-template-columns: auto;
}