tooltip1.css

[data-tip] {
  position: relative;
}

tooltip2.css

[data-tip]:before {
  content: '';
  position: absolute;
  top: 100%;
  left: calc(50% - 6px);
  margin-top: -6px;
  pointer-events: none;
  border: 6px solid transparent;
  border-bottom-color: #333;
}

tooltip3.css

[data-tip]:after {
  content: attr(data-tip);
  position: absolute;
  top: 100%;
  left: 50%;
  margin-top: 6px;
  background-color: #333;
  color: #fff;
  border-radius: 4px;
  white-space: nowrap;
  font-size: 0.8em;
  padding: 0.5em 1em;
  z-index: 100;
  transform: translate(-50%, 0);
}

tooltip4.css

[data-tip]:before,
[data-tip]:after {
  position: absolute;
  top: 100%;
  z-index: 100;
  visibility: hidden;
  opacity: 0;
}

tooltip5.css

[data-tip]:hover:before,
[data-tip]:hover:after {
  visibility: visible;
  opacity: 1;
}