JSFiddle - React, Tailwind, and code Playground

HTML

<html>
 <head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
  <title>Поля</title>
 </head>
 <body>
  <div class="box1">
    66% родителя
  </div>
  <div class="box2">
    66% родителя
  </div>
 </body>
</html>

CSS

.box1 {
width: 66%;
padding: 20px;
margin-bottom: 10px;
margin-left: 10px;
margin-right: 34%-10px;
border: 1px solid black;
background-color: yellow;
text-align: center;
}

.box2 {
margin-bottom: 10px;
margin-right: 10px;
margin-left: 34%;
width: 66%;
padding: 20px;
border: 1px solid black;
background-color: pink;
text-align: center;
    }