<div class="wrapper">
  <section class="column">This will stretch</section>
  <section class="column column--shrunk">This will not stretch because it has "align-self: start"</section>
</div>
.wrapper {
  background: #121212;
  border: 3px solid #121212;
  color: white;
  display: flex;
  flex-direction: row;
  font-family: 'Arial';
  height: 300px;
}

.column {
  background: #ff4163;
  margin: 15px;
  padding: 15px;
  width: 50%;
}

.column--shrunk {
  align-self: start;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.