HTML Code

<!DOCTYPE html>
<html lang=en>
<head>
  <meta charset=UTF-8>
  <meta name=viewport content="width=device-width,initial-scale=1">
  <title>marginheight — dynamic spacing</title>
  <style>body{font-family:system-ui,sans-serif;margin:0;padding:1.5rem;background:#f8fafc;color:#334155;line-height:1.7}h1{margin:0 0 .75rem;font-size:1.25rem;color:#0f172a}label{display:block;margin:.75rem 0 .35rem;font-size:.875rem;font-weight:500}input[type=range]{width:100%;max-width:320px}.frame-wrap{display:inline-block;padding:12px 0;background:#e2e8f0;border:2px solid #64748b;border-radius:8px;margin-top:.5rem}iframe{display:block;border:0;width:300px;height:72px}.status{margin-top:.75rem;font-size:.8125rem;color:#64748b;max-width:520px}code{background:#e2e8f0;padding:.1rem .35rem;border-radius:4px}</style>
</head>
<body>
  <h1>Adjust vertical spacing</h1>
  <label for=spaceRange>Wrapper padding (CSS): <span id=val>12</span>px</label>
  <input type=range id=spaceRange min=0 max=48 value=12>
  <div class=frame-wrap id=wrap>
    <iframe id=demoFrame srcdoc="&lt;!DOCTYPE html&gt;&lt;html&gt;&lt;body style='margin:0;font-family:system-ui;padding:6px;background:#dbeafe;'&gt;Iframe content&lt;/body&gt;&lt;/html&gt;" title="Adjustable spacing demo">
    </iframe>
  </div>
  <p class=status id=status>CSS <code>padding</code> on the wrapper updates spacing reliably. Legacy <code>iframe.marginHeight</code> is deprecated.</p>

  <script>var wrap=document.getElementById("wrap"),range=document.getElementById("spaceRange"),val=document.getElementById("val"),frame=document.getElementById("demoFrame");range.addEventListener("input",(function(){var e=range.value;val.textContent=e,wrap.style.padding=e+"px 0",frame.marginHeight=e}))</script>
</body>
</html>

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HTML marginheight Attribute — Adjust Spacing with JavaScript