@wordpress/block-library/build-style/footnotes/style.css

Block library for the WordPress editor.

.editor-styles-wrapper,
.entry-content {
  counter-reset: footnotes;
}

a[data-fn].fn {
  vertical-align: super;
  font-size: smaller;
  counter-increment: footnotes;
  display: inline-flex;
  text-decoration: none;
  text-indent: -9999999px;
}

a[data-fn].fn::after {
  content: "[" counter(footnotes) "]";
  text-indent: 0;
  float: left;
}