WordPress/wp-includes/blocks/footnotes/style.min.css

.editor-styles-wrapper,.entry-content{counter-reset:footnotes}a[data-fn].fn{counter-increment:footnotes;display:inline-flex;font-size:smaller;text-decoration:none;text-indent:-9999999px;vertical-align:super}a[data-fn].fn:after{content:"[" counter(footnotes) "]";float:left;text-indent:0}