popper js example

#tooltip[data-popper-placement^='top'] > #arrow {
  bottom: -4px;
}

#tooltip[data-popper-placement^='bottom'] > #arrow {
  top: -4px;
}

#tooltip[data-popper-placement^='left'] > #arrow {
  right: -4px;
}

#tooltip[data-popper-placement^='right'] > #arrow {
  left: -4px;
}<div id="tooltip" role="tooltip">
  My tooltip
  <div id="arrow" data-popper-arrow></div>
</div>#arrow,
#arrow::before {
  position: absolute;
  width: 8px;
  height: 8px;
  z-index: -1;
}

#arrow::before {
  content: '';
  transform: rotate(45deg);
  background: #333;
}