HTML Code

<!DOCTYPE html>
<html lang=en>
<head>
  <meta charset=UTF-8>
  <meta name=viewport content="width=device-width,initial-scale=1">
  <title>Form Output</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 1rem;font-size:1.25rem;color:#0f172a}form{display:flex;flex-wrap:wrap;align-items:center;gap:.5rem .65rem;padding:1rem;background:#fff;border:1px solid #cbd5e1;border-radius:8px;max-width:420px}input[type=number]{width:4.5rem;padding:.35rem .5rem;border:1px solid #cbd5e1;border-radius:6px;font:inherit}output{font-weight:700;font-size:1.125rem;color:#0f172a}.hint{margin-top:1rem;font-size:.8125rem;color:#64748b}</style>
</head>
<body>
  <h1>Form sum</h1>
  <form oninput="result.value=parseInt(num1.value,10)+parseInt(num2.value,10)">
    <input type=number id=num1 name=num1 value=10 min=0 aria-label="First number">
    <span>+</span>
    <input type=number id=num2 name=num2 value=20 min=0 aria-label="Second number">
    <span>=</span>
    <output name=result for="num1 num2">30</output>
  </form>
  <p class=hint>Change either number to see the output update.</p>
</body>
</html>

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HTML output Tag — Form-Related Output