<!doctype html>
<html>
    <head>
        <style>
            fieldset > div { border:2px solid skyblue; background-color:#cccccc; margin-block-start:6px; margin-block-end:6px  }
            fieldset { margin:0; vertical-align:bottom; inline-size:320px; block-size:80px; display:flex; justify-content: center; align-items: stretch; background-color:#dddddd; border:12px solid navy; padding:28px }
            </style>
    </head>
    <body>
        <fieldset>
            <legend>Legend</legend>
            <div>Fieldset Contents</div>
            
            <div>More Fieldset Contents</div>
            
        </fieldset>
    </body>
</html>