<!DOCTYPE HTML>
<style>
body {
  background-color: green;
}

#thediv {
  width: 300px;
  height: 100px;
  position: absolute;
  top: 20px;
  left: 20px;
  opacity: 0.6;
  box-shadow: 3px 3px 2px rgb(255,0,0);
}
</style>

<div id="thediv"></div>