Demo: CSS column-rule-color

<div class='container'>
  <p>Column 1</p>
  <p>Column 2</p>
  <p>Column 3</p>
</div>

.container {
  column-count: 3;
  column-rule: 2px solid #333;
  column-rule-color: blue;
}

// No JavaScript required for this demo

Column 1

Column 2

Column 3