body {
  background: #eee;
  font-family: sans-serif;
}

h1 {
  font-size: 1rem;
}

.compare {
  background: #fff;
  margin: 1rem;
  padding: 1rem;
}

.dom, .math {
  display: inline-block;
  margin-right: 1rem;
}

.parent {
  background: #ddd;
  position: relative;
  overflow: hidden;
}

.child {
  display: block;
}

.dom .child {
  width: 100%;
  height: 100%;
  background: #39f;
}

.math .parent {
  background: #39f;
}

.math .child {
  position: absolute;
}