.footnotes {
  li {
    position: relative;

    .footnote-backref {
      position: absolute;
      top: 0;
      left: 0;
      transform: translateX(-250%);
      opacity: 0;
    }

    &:hover .footnote-backref {
      opacity: 1;
    }
  }
}

Move footnote backrefs to gutter hover links
Move footnote backrefs to gutter hover links
