JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="sidebar">Блок 1</div>
  <div class="content">Блок 2</div>
  <div class="third-block">Блок 3</div>
</div>

CSS

.container {
  max-width: 300px;
  color: #fff;
}
.sidebar, .content {
  min-height: 150px;
}
.sidebar {
  width: 100px;
  float: left;
  background: #f00;
}
.content{
  overflow: hidden;
  background: #00f;
}
.third-block {
  clear: both;
  min-height: 100px;
  background: #0f0;
}