Font-Awesome/free/less/_stacked.less

// stacking icons
// -------------------------

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

.@{fa-css-prefix}-stack-1x, .@{fa-css-prefix}-stack-2x {
  left: 0;
  position: absolute;
  text-align: center;
  width: 100%;
  z-index: ~'var(--@{fa-css-prefix}-stack-z-index, @{fa-stack-z-index})';
}

.@{fa-css-prefix}-stack-1x { 
  line-height: inherit; 
}

.@{fa-css-prefix}-stack-2x { 
  font-size: 2em; 
}

.@{fa-css-prefix}-inverse { 
  color: ~'var(--@{fa-css-prefix}-inverse, @{fa-inverse})';
}