CSS based Molten Leading technique. by Mike Riethmuller, adapted from Wilto. Found from a CSS-Tricks email.

leading.css

.molten-leading {
  line-height: 1.2em;
}

@media screen and (min-width: 20em) {
  .molten-leading {
    line-height: calc(1.2em + 0.6 * ((100vw - 20em) / 60));
  }
}

@media screen and (min-width: 80em) {
  .molten-leading {
    line-height: 1.8em;
  }
}