I have created a table and would like to add html to a cell.  I have the data type as String with multi-line editing.  I am trying to add this code to the cell:

<div class="tooltip">Hover over me
  <span class="tooltiptext">This is the tooltip text!</span>
</div>

When I save it the cell looks blank and when I go back to edit the contents the code now looks like this:

<a href='<div class="tooltip">Hover over me
  <span class="tooltiptext">This is the tooltip text!
</div>' target='_self'><div class="tooltip">Hover over me
  <span class="tooltiptext">This is the tooltip text!
</div></a>

This is clearly bad HTML so the cell renders nothing.  Below is the Custom CSS that I have added to the settings page to make this tooltip work in case there are issues with that as well.  Please advise why this is happening.

Custom CSS:

.tooltip {
  position: relative;
  display: inline-block;
  border-bottom: 1px dotted black;
}

.tooltip .tooltiptext {
  visibility: hidden;
  width: 120px;
  background-color: #333;
  color: #fff;
  text-align: center;
  border-radius: 6px;
  padding: 5px 0;
  position: absolute;
  z-index: 1;
  bottom: 150%;
  left: 50%;
  margin-left: -60px;
}

.tooltip .tooltiptext::after {
  content: "";
  position: absolute;
  top: 100%;
  left: 50%;
  margin-left: -5px;
  border-width: 5px;
  border-style: solid;
  border-color: black transparent transparent transparent;
}

.tooltip:hover .tooltiptext {
  visibility: visible;
}

Sam