<!doctype html>
<style type='text/css'>
  #grid {
    display: grid;
    grid-template-rows: [row1-start] auto [row2-start] auto [row2-end];
    grid-template-columns: [col1-start] 100px [col2-start] 100px [col3-start] 100px [col3-end];
  }
  #cell3 {
    grid-column: "col3-start";
    grid-row: "row2-start";
  }
</style>
<div id="grid">
  <div>cell1</div>
  <div id="cell2">cell2</div>
  <div id="cell3">cell3</div>
</div>