<!DOCTYPE html>
<html>
  <meta charset="utf-8">
  <title>CSS Multi-column Layout Test Reference: Test the column rules' block-size with nested balancing multicol container</title>
  <link rel="author" title="Ting-Yu Lin" href="tlin@mozilla.com">
  <link rel="author" title="Mozilla" href="https://www.mozilla.org/">

  <style>
  .outer {
    column-count: 2;
    column-rule: 6px solid black;
    column-fill: auto;
    width: 400px;
    height: 250px;
  }
  .inner {
    column-count: 2;
    column-rule: 3px solid gray;
    column-fill: auto;
    height: 200px;
  }
  .outer-block {
    background-color: lightgreen;
    height: 200px;
  }
  .inner-block {
    background-color: lightblue;
    height: 200px;
  }
  .space {
    height: 50px;
  }
  </style>

  <article class="outer">
    <div class="outer-block"></div>
    <div class="space"></div>
    <article class="inner">
      <div class="inner-block"></div>
      <div class="inner-block"></div>
    </article>
  </article>
</html>