JSFiddle - React, Tailwind, and code Playground

HTML

<body>
  <div class="row">
    <input type="button" value="1">
    <input type="button" value="2">
    <input type="button" value="3">
    <input type="button" value="4">
  </div>
  <div class="row">
    <input class="long-width" type="button" value="0">
    <input type="button" value=".">
    <input type="button" value="=">
  </div>
</body>

CSS

input[type="button"] {
  width: 20%;
  height: 30px;
  font-size: 15px;
  border-radius: 5px;
}

input[type="button"].long-width {
  width: 45%;
}