JSFiddle - React, Tailwind, and code Playground

HTML

<body>
<div class="a1">
  <div class="a2">
    текст
  </div>
  <div class="a3">
    текст
  </div>
  <div style="clear:both;">
  
  </div>
</div>
</body>

CSS

.a1 {
  width: 700px;
  border: 1px solid red;
}

.a2 {
  float: left;
  width: 25%;
  background-color: #ccc;
  height: 300px;
}

.a3 {
  float: left;
  width: 65%;
  background-color: #fff;
  height: 100%;
}