A simple CSS-only text popover

This is some text

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<a data-title="hello, world" href="...">...</a>

a[data-title] {
  position: relative;
  display: inline-block;
  margin-top: 1rem;
}

Other words here

a[data-title]:hover::after {
  content: attr(data-title);
  position: absolute;
  background-color: black;
  color: white;
  top: -1.7rem;
  left: -2rem;
  padding: 0.1rem 0.4rem;
  border-radius: 5px;
}