@thebase/ui/dist/runtime/milkdown/theme/common/placeholder.css

CDN-installable Owl and Bootstrap 5 UI component library.

.milkdown .crepe-placeholder::before {
    position: absolute;
    color: color-mix(
      in srgb,
      var(--crepe-color-on-background),
      transparent 60%
    );
    pointer-events: none;
    height: 0;
    content: attr(data-placeholder);
  }