weseek__growi/resource/styles/bootstrap4/mixins/_text-hide.scss

// CSS image replacement
@mixin text-hide() {
  // stylelint-disable-next-line font-family-no-missing-generic-family-keyword
  font: 0/0 a;
  color: transparent;
  text-shadow: none;
  background-color: transparent;
  border: 0;
}