JSFiddle - React, Tailwind, and code Playground

HTML

<div class="FlexOuterContainer">
  <div class="FlexInnerContainer">
    <div class="FlexItem">MMMMM</div>
    <div class="FlexItem">MMMMM</div>
  </div>
</div>

CSS

.FlexOuterContainer {
  border: 3px solid black;
  display: flex;
  margin: 1em;
}
.FlexInnerContainer {
  border: 3px solid red;
  display: flex;
  flex: 0 0 auto;
}
.FlexItem {
  background: rgba(0,0,0,.2);
  flex: 0 0 100px;
}