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<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>Dynamic class 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 1rem;font-size:1.25rem;color:#0f172a}.dynamic-style{color:red;font-weight:700}.hint{margin-top:1rem;font-size:.8125rem;color:#64748b;max-width:480px}</style>

</head>

<body>

  <h1>classList.add</h1>

  <p id=dynamicElement>This text will get a new style dynamically.</p>

  <p class=hint>JavaScript adds <code>dynamic-style</code> with <code>element.classList.add("dynamic-style")</code>.</p>

  <script>document.getElementById("dynamicElement").classList.add("dynamic-style")</script>

</body>

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HTML class Attribute — Dynamic classList