robertjohnson.work/assets/plugins/font-awesome/less/_stacked.less

// Stacked Icons
// -------------------------

.@{fa-css-prefix}-stack {
  display: inline-block;
  height: 2em;
  line-height: 2em;
  position: relative;
  vertical-align: middle;
  width: 2em;
}

.@{fa-css-prefix}-stack-1x, .@{fa-css-prefix}-stack-2x {
  left: 0;
  position: absolute;
  text-align: center;
  width: 100%;
}

.@{fa-css-prefix}-stack-1x { line-height: inherit; }
.@{fa-css-prefix}-stack-2x { font-size: 2em; }
.@{fa-css-prefix}-inverse { color: @fa-inverse; }