.copy-button {
  position: absolute;
  display: none;
  cursor: pointer;
  inset: 5px 5px auto auto;
  width: 1em;
  height: 1em;
  border: 1px solid;
  box-shadow: -3px 3px #999;
}
:is(:focus, :hover) > .copy-button {
  display: inline-block;
}
.copy-success {
  box-shadow: none;
  background: #999;
  transition: box-shadow 300ms ease-out, background 300ms ease-out;
}
.copy-fail {
  border-style: dotted;
}