.back-btn {
  position: fixed;
  top: 20px;
  left: 20px;
  z-index: 100;
  display: block;
  width: 254px;
  height: 40px;
  line-height: 0;
}
.back-btn img { display: block; width: 254px; height: 40px; }
.back-btn .back-hover { position: absolute; top: 0; left: 0; opacity: 0; transition: opacity 0.15s ease; }
.back-btn:hover .back-hover { opacity: 1; }