JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <link rel="stylesheet" href="index.css">
  <title>CSS Tests</title>
</head>
<body>

  <div class="div2">
    <input type="Foobar">
  </div>
</body>
</html>

CSS

body {
  margin: 0;
}

.div2 {
  width: 100%;
  height: 100px;
  background-color:indianred;
}

.div2 input {
  /*width: 100%;*/
  width: calc(100% - 20px);
  margin: 10px;
  box-sizing: border-box;
}