JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
  <p>
   HTML FORUM
  </p>
  <div class="input">
    <input type="text" size="20">
  </div>
</div>

CSS

* {
  margin: 0px;
  padding: 0px;
}
.main {
  border: 1px solid black;
  height: 80px;
}
.main .input {
  max-width:300px;
}
.input input {
  width: 100%;
}