JSFiddle - React, Tailwind, and code Playground

HTML

<div class="block">
  <div class="item item-1">100</div>
  <div class="item item-2">200</div>
</div>

SCSS

.block {
  width: 500px;
  height: 200px;
  display: flex;
  background: lightgray;
  margin: auto;
  & .item {
    background: gray;
    &.item-1 {
      flex: 0 1 100px
    }
    &.item-2 {
      flex: 0 1 200px
    }
  }
}