JSFiddle - React, Tailwind, and code Playground

HTML

<body>
  <div class="box1">box1</div>
  <br>
  <div class="box2">box2</div>
</body>

CSS

.box1{
  width: 100px;
  height: 100px;
  background: red;
  padding:5px;
  border:5px solid gray;
}
.box2{
  width: 100px;
  height: 100px;
  background: red;
  padding:5px;
  border:5px solid gray;
  box-sizing: border-box; 
}