permalink.css

h2, h3, h4, h5, h6 {
  position: relative;
}

.permalink {
  position: absolute;
  left: -0.5em;
  opacity: 0;

  -webkit-transition: opacity 0.2s ease-in-out 0.1s;
  transition: opacity 0.2s ease-in-out 0.1s;
}

h2:hover .permalink,
h3:hover .permalink,
h4:hover .permalink,
h5:hover .permalink,
h6:hover .permalink {
  opacity: 1;
}