article { counter-reset: footnotes; }
a.footnote {
  counter-increment: footnotes;
  text-decoration: none;
  color: inherit;
  cursor: default;
  outline: none;
}
a.footnote::after {
  content: '[' counter(footnotes) ']';
  vertical-align: super;
  font-size: 0.5em;
  margin-left: 2px;
  color: blue;
  text-decoration: underline;
  cursor: pointer;
}
a.footnote:focus::after {
  outline: thin dotted;
  outline-offset: 2px;
}
footer li {
  font-size: 0.75em;
}
footer li :target {
  background: yellow;
}