Use width in pixels for desktop size and then add max-width:100% so it can’t go wider than mobile viewport:

<div class="content-item brand-space-top-small" style="margin-bottom:1.7rem;">      

    <img src="https://nwscdn.com/media/wysiwyg/buyersguide/US_goal_sizes.jpg" style="width:1000px; max-width: 100%;" alt="US Soccer goal sizes" />

  </div>