Tri-element centered row

HTML

<section class="tri-element-rows">
  <div class="left-element"></div>
  <div class="middle-element"></div>
  <div class="right-element"></div>
</section>

<section class="tri-element-rows">
  <div class="left-element"></div>
  <div class="middle-element"></div>
  <div class="right-element"></div>
</section>

CSS

html, body {
  height: 100%
}
section {
  display: flex;
  height: 50%;
}

div.middle-element {
  width: 15rem;
  height: 10rem;
}

div.left-element,
div.right-element {
  flex-grow: 1;
}

div {
  background-color: coral;
  margin: 1rem;
}