<div style="column-count: 3; 
     column-rule: solid blue 0.3em; column-gap: 0.3em">
  <h1 style="column-span: all">An imporant element</h1>
  <p>...</p>
  <h2 style="column-span: 2">A not-so important element</h2>
  <p>...</p>
</div>