thetool/public/fontawesome/scss/_widths.scss

// icon widths
// -------------------------
@use 'variables' as v;

.#{v.$css-prefix}-width-auto {
  --#{v.$css-prefix}-width: auto;
}

.#{v.$css-prefix}-fw,
.#{v.$css-prefix}-width-fixed {
  --#{v.$css-prefix}-width: #{v.$fw-width};
}