Font-Awesome/js-packages/@fortawesome/fontawesome-free/scss/_screen-reader.scss

// screen-reader utilities
// -------------------------

// only display content to screen readers
.sr-only,
.#{$fa-css-prefix}-sr-only {
  @include fa-sr-only;
}

// use in conjunction with .sr-only to only display content when it's focused
.sr-only-focusable,
.#{$fa-css-prefix}-sr-only-focusable {
  @include fa-sr-only-focusable;
}