<!DOCTYPE html>
<html>
  <head>
  <style>
    * {
      padding: 0;
      margin: 0;
    }
    .flexible-grid {
      display: grid;
      width: 100%;
      height: 100vh;
    }
  </style>
  </head>
  <body>
    <div class="flexible-grid">
      <div
        class="flexible-grid-item"
        data-name="first"
        data-row-start="1"
        data-row-width="1"
        data-col-start="1"
        data-col-width="2"
      >
        First element
      </div>
      <div
        class="flexible-grid-item"
  