mj-wrapper-background.mjml

<mjml>
  <mj-body>
    <mj-wrapper background-color="red" background-repeat="no-repeat" background-size="contain" background-url="https://www.rust-lang.org/static/images/rust-logo-blk.svg">
      <mj-section></mj-section>
    </mj-wrapper>
  </mj-body>
</mjml>