<style>
  body {
    padding: 40px;
  }

  article {
    --aside-width: 6em;
    display: grid;
    grid-template-columns: 1fr repeat(2, minmax(auto, var(--aside-width)));
    grid-template-rows: auto 1fr auto;
    min-height: 100vh;
    max-width: 60em;
    margin: 0 auto;
  }

  header {
    border: 2px solid black;
    border-bottom: 0;
    padding: 24px 24px 0;
    grid-column: 1 / 3;
    grid-row: 1 / 1;
  }

  article .content,
  aside {
    background: white;
    padding: 24px;
    border: 2px solid black;
    grid-row: 2;
  }

  article .content {
    grid-column: 1 / 3;
    border-top: none;

    > * {
      padding-right: var(--aside-width);
    }
  }

  aside {
    grid-column: 2 / 4;
    margin: 24px 0 40px;
  }

  article header {
    h1 {
      font-size: 3rem;
      font-weight: bold;
    }
  }

  @media (max-width: 55em) {
    article .content,
    aside,
    header {
      grid-column: span 4;
      grid-row: auto;
    }

    article .content {
      > * {
        padding: 0;
      }
    }

    aside {
      margin: 24px 0;
    }
  }
</style>

<article>
  <header>
    <h1>Title that can be really long if it really wants to be</h1>
  </header>
  <div class="content">
    <p>
      The first nuclear device was detonated as a test by the United States at
      the Trinity site on July 16, 1945, with a yield approximately equivalent
      to 20 kilotons of TNT. The first thermonuclear weapon technology test of
      engineer device, codenamed "Ivy Mike", was tested at the Enewetak atoll in
      the Marshall Islands on November 1, 1952 (local date), also by the United
      States. The largest nuclear weapon ever tested was the "Tsar Bomba" of the
      Soviet Union at Novaya Zemlya on October 30, 1961, with the largest yield
      ever seen, an estimated 50–58 megatons. The first nuclear device was
      detonated as a test by the United States at the Trinity site on July 16,
      1945, with a yield approximately equivalent to 20 kilotons of TNT. The
      first thermonuclear weapon technology test of engineer device, codenamed
      "Ivy Mike", was tested at the Enewetak atoll in the Marshall Islands on
      November 1, 1952 (local date), also by the United States. The largest
      nuclear weapon ever tested was the "Tsar Bomba" of the Soviet Union at
      Novaya Zemlya on October 30, 1961, with the largest yield ever seen, an
      estimated 50–58 megatons. The first nuclear device was detonated as a test
      by the United States at the Trinity site on July 16, 1945, with a yield
      approximately equivalent to 20 kilotons of TNT. The first thermonuclear
      weapon technology test of engineer device, codenamed "Ivy Mike", was
      tested at the Enewetak atoll in the Marshall Islands on November 1, 1952
      (local date), also by the United States. The largest nuclear weapon ever
      tested was the "Tsar Bomba" of the Soviet Union at Novaya Zemlya on
      October 30, 1961, with the largest yield ever seen, an estimated 50–58
      megatons.
    </p>
  </div>

  <aside>Aside</aside>
</article>