JSFiddle - React, Tailwind, and code Playground

HTML

<div class="row">
  <div class="col line">
    
  </div>
  <div class="col second">
    hello
  </div>
  <div class="col second">
    goodbye
  </div>
</div>

CSS

* {
  outline: 1px solid red
}

.row {
  background-color: lightblue;
  height: 200px;
  box-sizing: border-box;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-flex: 0;
  -ms-flex: 0 1 auto;
  flex: 0 1 auto;
  -webkit-box-orient: horizontal;
  -webkit-box-direction: normal;
  -ms-flex-direction: row;
  flex-direction: row;
  -ms-flex-wrap: wrap;
  flex-wrap: wrap;
}

.col {
  flex-basis: 100%;
  max-width: 100%;
}

.line {
  background-color: blue;
  height: 10px;
}

.second {
  background-color: #EEE8AA;
}