body {
  background-color: #F5F5F5;
  color: #555;
  font-size: 1.1em;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

.container {
  margin: 40px auto;
  max-width: 700px;
}

.element {
  width: 200px;
  height: 200px;
  background-color: #009966;
  opacity: .8;
  position: relative;
  margin: 100px auto;
}

.element:before {
  position: absolute;
  content: "";
  display: block;
  width: 100%;
  height: 100%;
  background-color: #009966;
  opacity: .8;
  -webkit-transform: rotateZ(45deg);
  transform: rotateZ(45deg);
}