JSFiddle - React, Tailwind, and code Playground

HTML

<body>
  <div id='box2' class='box'></div>
</body>

CSS

body {
  background: url(http://ruby-china.org/assets/bg-ee85ccdd05884ebba8b9c2fab569e690.png);
}

.box {
  width: 200px;
  height: 200px;
}

#box2 {
    position: absolute;
    left: 100px;
    top: 100px;
    background: rgba(0, 0, 255, 0.3);
}