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<h1 style="font-size:20px;">Thẻ h1</h1>
<h2 style="font-size:20px;">Thẻ h2</h2>
<h3 style="font-size:20px;">Thẻ h3</h3>
<h4 style="font-size:20px;">Thẻ h4</h4>
<h5 style="font-size:20px;">Thẻ h5</h5>
<h6 style="font-size:20px;">Thẻ h6</h6>