body {
  background-color: white;
}

.el {
  width: 200px;
}
.el:after {
  position: fixed;
  z-index: 100;
  font-family: Helbetica;
  content: "test text";
  display: block;
  font-size: 50px;
  padding: 10px 20px;
  mix-blend-mode: revert;
}

body {
  height: 100%;
}