Edit in JSFiddle

<div class="parent">
  <div class="child">Hello World!</div>
</div>

.parent {
  height: 100px;
  width: 100%;
  border: 2px dashed #f69c55;
  position: relative;
}

.child {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}