chromium/src/third_party/blink/renderer/core/testing/data/rgm_column_test.html

<style>
  .colStyle {
      -webkit-column-count: 3;
      -webkit-column-gap:10px;
  }
</style>

<div id='A' class='colStyle'>
  <div id='Col1'> A </div>
  <div> A </div>
  <div> A </div>
  <div id='Col2'> A </div>
  <div> A </div>
  <div> A </div>
  <div id='Col3'> A </div>
</div>