CSS-only animated tooltips

tooltip.css

/* Originally by Chris Bracco with a few cleanups and fixes http://cbracco.me/a-simple-css-tooltip/ */

/* Base styles for the element that has a tooltip */
[tooltip],
.tooltip {
  position: relative;
  cursor: pointer;
}

/* Base styles for the entire tooltip */
[tooltip]::before,
[tooltip]::after,
.tooltip::before,
.tooltip::after {
  position: absolute;
  visibility: hidden;
  opacity: 0;
  transition:         
    opacity 0.2s ease-in-out,
    visibility 0.2s ease-in-out,
    transform 0.2s cubic-bezier(0.71, 1.7, 0.77, 1.24);
  transform: translate3d(0, 0, 0);
  pointer-events: none;
}

/* Show the entire tooltip on hover and focus */
[tooltip]:hover::before,
[tooltip]:hover::after,
[tooltip]:focus::before,
[tooltip]:focus::after,
.tooltip:hover::before,
.tooltip:hover::after,
.tooltip:focus::before,
.tooltip:focus::after {
  visibility: visible;
  opacity: 1;
}

/* Base styles for the tooltip's directional arrow */
.tooltip::before,
[tooltip]::before {
  z-index: 1001;
  border: 6px solid transparent;
  background: transparent;
  content: "";
}

/* Base styles for the tooltip's content area */
.tooltip::after,
[tooltip]::after {
  z-index: 1000;
  padding: 8px;
  width: 160px;
  background-color: #000;
  background-color: hsla(0, 0%, 20%, 0.9);
  color: #fff;
  content: attr(tooltip);
  font-size: 14px;
  line-height: 1.2;
}

/* Directions */

/* Top (default) */
[tooltip]::before,
[tooltip]::after,
.tooltip::before,
.tooltip::after,
.tooltip-top::before,
.tooltip-top::after {
  bottom: 100%;
  left: 50%;
}

[tooltip]::before,
.tooltip::before,
.tooltip-top::before {
  margin-left: -6px;
  margin-bottom: -12px;
  border-top-color: #000;
  border-top-color: hsla(0, 0%, 20%, 0.9);
}

/* Horizontally align top/bottom tooltips */
[tooltip]::after,
.tooltip::after,
.tooltip-top::after {
  margin-left: -80px;
}

[tooltip]:hover::before,
[tooltip]:hover::after,
[tooltip]:focus::before,
[tooltip]:focus::after,
.tooltip:hover::before,
.tooltip:hover::after,
.tooltip:focus::before,
.tooltip:focus::after,
.tooltip-top:hover::before,
.tooltip-top:hover::after,
.tooltip-top:focus::before,
.tooltip-top:focus::after {
  transform: translateY(-12px); 
}

/* Left */
.tooltip-left::before,
.tooltip-left::after {
  right: 100%;
  bottom: 50%;
  left: auto;
}

.tooltip-left::before {
  margin-left: 0;
  margin-right: -12px;
  margin-bottom: 0;
  border-top-color: transparent;
  border-left-color: #000;
  border-left-color: hsla(0, 0%, 20%, 0.9);
}

.tooltip-left:hover::before,
.tooltip-left:hover::after,
.tooltip-left:focus::before,
.tooltip-left:focus::after {
  transform: translateX(-12px); 
}

/* Bottom */
.tooltip-bottom::before,
.tooltip-bottom::after {
  top: 100%;
  bottom: auto;
  left: 50%;
}

.tooltip-bottom::before {
  margin-top: -12px;
  margin-bottom: 0;
  border-top-color: transparent;
  border-bottom-color: #000;
  border-bottom-color: hsla(0, 0%, 20%, 0.9);
}

.tooltip-bottom:hover::before,
.tooltip-bottom:hover::after,
.tooltip-bottom:focus::before,
.tooltip-bottom:focus::after {
  transform: translateY(12px); 
}

/* Right */
.tooltip-right::before,
.tooltip-right::after {
  bottom: 50%;
  left: 100%;
}

.tooltip-right::before {
  margin-bottom: 0;
  margin-left: -12px;
  border-top-color: transparent;
  border-right-color: #000;
  border-right-color: hsla(0, 0%, 20%, 0.9);
}

.tooltip-right:hover::before,
.tooltip-right:hover::after,
.tooltip-right:focus::before,
.tooltip-right:focus::after {
  transform: translateX(12px); 
}

/* Move directional arrows down a bit for left/right tooltips */
.tooltip-left::before,
.tooltip-right::before {
  top: 3px;
}

/* Vertically center tooltip content for left/right tooltips */
.tooltip-left::after,
.tooltip-right::after {
  margin-left: 0;
  margin-bottom: -16px;
}

tooltip.html

<p class="tooltip-bottom" tooltip="I’m the tooltip text.">Tooltip</p>