nopaque/app/static/sass/components/_service-icon.scss

@each $service, $letter in $service-icon-letters {
  .nopaque-icons.service-icons[data-service="#{$service}"]:empty::before,
  [data-service="#{$service}"] .nopaque-icons.service-icons[data-service="inherit"]:empty::before {
    content: "#{$letter}";
  }
}