JSFiddle - React, Tailwind, and code Playground

HTML

<div class="row example">
  <div class="col">A</div>
  <div class="double col">B</div>
</div>

<div class="row example">
  <div class="col">A</div>
  <div class="col">B</div>
  <div class="col">C</div>
</div>

<div class="row example">
  <div class="double col">A</div>
  <div class="col">B</div>
</div>

CSS

.row {
	display: flex;
	flex-wrap: wrap;
}

.col {
	box-sizing: border-box;
	flex: 1;
}

.double { flex: 2; }

/* --------------------- */

.example .col {
  background: blue;
  /*border: solid 2px yellow;*/
  /*margin: 10px;*/
  padding: 10px;
  color: white;
  text-align: center;
  height: 50px;
}

.example .col:nth-child(odd) {
  background: #08f;
}