کادرهای واکنشگرا

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  <p>London is the most populous city in the United Kingdom,
  with a metropolitan area of over 9 million inhabitants.</p>
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  <p>London is the most populous city in the United Kingdom,
  with a metropolitan area of over 9 million inhabitants.</p>
</div>

<div class="w3-panel w3-pale-blue w3-leftbar w3-rightbar w3-border-blue">
  <p>London is the most populous city in the United Kingdom,
  with a metropolitan area of over 9 million inhabitants.</p>
</div>

<div class="w3-panel w3-pale-red w3-leftbar w3-border-red">
  <p>London is the most populous city in the United Kingdom,
  with a metropolitan area of over 9 million inhabitants.</p>
</div>

<div class="w3-panel w3-pale-yellow w3-border w3-border-yellow">
  <p>London is the most populous city in the United Kingdom,
  with a metropolitan area of over 9 million inhabitants.</p>
</div>

<div class="w3-panel w3-pale-green w3-bottombar w3-border-green w3-border">
  <p>London is the most populous city in the United Kingdom,
  with a metropolitan area of over 9 million inhabitants.</p>
</div>

<div class="w3-panel w3-yellow w3-topbar w3-bottombar w3-border-amber">
  <p>London is the most populous city in the United Kingdom,
  with a metropolitan area of over 9 million inhabitants.</p>
</div>