<h1>Tiêu đề 1</h1>
<h2>Tiêu đề 2</h2>
<h3>Tiêu đề 3</h3>
h1{

  background-color: red;

  opacity: 0.5;

}

h2{

  background-color: red;

  opacity: 0.7;

}
h3{

  background-color: red;

  opacity: 1;

}

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