JSFiddle - React, Tailwind, and code Playground

HTML

<body>
  <header>  
</header>
<section>
  <div class="holder">
    
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Doloribus quibusdam nisi consequuntur numquam quas eligendi temporibus, ex, quos dolorum sequi laboriosam voluptatibus, rerum dolor modi repudiandae odit amet, eius autem.</p>
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Delectus omnis reiciendis nesciunt corporis nam facere, repudiandae qui debitis, cupiditate dolor suscipit voluptatibus dolores quam earum consequuntur rerum assumenda ab cum!</p>
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Non nihil ipsam, consectetur earum quisquam nostrum, obcaecati, neque quo quas voluptatum cum ab fugit doloremque placeat officia sapiente quibusdam porro fuga.</p>

  </div>
</section>
</body>

CSS

html,
body {
  
  background:  url("картинка") no-repeat center center;
  background: #cccccc;
  overflow: hidden;
  height: 100%;
  margin: 0;
}
header {
    position: relative;
    height: 70px;
    background-color: rgba(42, 50, 130, 0.8);
    top: 0;
    left: 0;
    z-index: 1;
    width: 100%;
    padding: 0;
}
section {
  height: calc(100% - 70px);
  box-sizing: border-box;
  overflow: auto;
}

.holder {
  height: 100em;
}