JSFiddle - React, Tailwind, and code Playground

HTML

<section>
  <div></div>
  <div></div>
  <div></div>
</section>

SCSS

section {
  display: flex;
  background: springgreen;
  border: 1px dashed slategray;
  height: 200px;
  
  div {
    &:first-child {
      background: lightsteelblue;
      flex: 1 0 100px;
    }
    &:nth-child(2) {
      background: lightgreen;
      flex: 10 0 400px;
    }
    &:last-child {
      background: palegoldenrod;
      flex: 1 0 100px;
      display: none;
    }
  }
}