Font-Awesome/less/_core.less

// base icon class definition
// -------------------------

.@{fa-css-prefix} {
  font-family: ~'var(--@{fa-css-prefix}-style-family, @{fa-style-family})';
  font-weight: ~'var(--@{fa-css-prefix}-style, @{fa-style})';
}

.@{fa-css-prefix},
.fas,
.@{fa-css-prefix}--solid,
.far,
.@{fa-css-prefix}--regular,
.fal,
.@{fa-css-prefix}--light,
.fat,
.@{fa-css-prefix}--thin,
.fad,
.@{fa-css-prefix}--duotone,
.fab,
.@{fa-css-prefix}--brands {
  -moz-osx-font-smoothing: grayscale;
  -webkit-font-smoothing: antialiased;
  display: ~'var(--@{fa-css-prefix}-display, @{fa-display})';
  font-style: normal;
  font-variant: normal;
  text-rendering: auto;
}