HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

  <meta name=viewport content="width=device-width,initial-scale=1">

  <title>width — JavaScript example</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}#dynamicElement{height:4rem;background:#dbeafe;border:1px solid #93c5fd;border-radius:6px;display:flex;align-items:center;justify-content:center;font-size:.875rem}button{margin-top:.75rem;margin-right:.5rem;padding:.45rem .85rem;border:1px solid #cbd5e1;border-radius:6px;background:#fff;cursor:pointer;font:inherit}.hint{font-size:.8125rem;color:#64748b;margin-top:.75rem}</style>

</head>

<body>

  <h1>Dynamic width</h1>



  <div id=dynamicElement>Resize me</div>



  <button type=button onclick='setWidth("200px")'>200px</button>

  <button type=button onclick='setWidth("50%")'>50%</button>



  <script>function setWidth(t){document.getElementById("dynamicElement").style.width=t}setWidth("200px")</script>



  <p class=hint>For responsive layouts, CSS <code>width</code> via JavaScript supports px, %, vw, and more.</p>

</body>

</html>

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HTML width Attribute — dynamic CSS width