JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
  <div class="sitebar">1</div>
  <div class="content">2</div>
</div>

CSS

.wrapper{
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
}
.sitebar {
  width: 200px;
  background-color: #cc0000;
}

.content {
  width: -webkit-calc(100vw - 200px);
  width: calc(100vw - 200px);
  background-color: #00cc00;
}