Basic CSS layout demio

HTML

<div width='100%' align='center'>
<div class='relative'>
    <div class='absolute'>
    </div>
</div>
</div>

CSS

.relative {
  position: static;
  width: 200px;
  height: 400px;
  background-color: red;
  margin-top: 50px;
}
.absolute {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: black;
  z-index: -10;
}