<div id="multicol">
  <div id="scrollable">
    <div style="height:200%;">
      This should be monolithic (unbreakable), since we're inside a scrollable
      container. So, even if it's very tall, it should only be in the first
      column.
    </div>
  </div>
</div>

#multicol {
  columns: 3;
  column-fill: auto;
  height: 80px;
  background: darkturquoise;
}
#scrollable {
  overflow-y: scroll;
  height: 200px;
  background: mediumseagreen;
}