bootstrap 4 tooltip
<button type="button" class="btn btn-secondary" data-toggle="tooltip" data-placement="top" title="Tooltip on top"> Tooltip on top </button> <button type="button" class="btn btn-secondary" data-toggle="tooltip" data-placement="right" title="Tooltip on right"> Tooltip on right </button> <button type="button" class="btn btn-secondary" data-toggle="tooltip" data-placement="bottom" title="Tooltip on bottom"> Tooltip on bottom </button> <button type="button" class="btn btn-secondary" data-toggle="tooltip" data-placement="left" title="Tooltip on left"> Tooltip on left </button> <button type="button" class="btn btn-secondary" data-toggle="tooltip" data-html="true" title="<em>Tooltip</em> <u>with</u> <b>HTML</b>"> Tooltip with HTML </button>