<details>
  <summary>HTML</summary>
  <p>HTML is Awesome and powerful.</p>
</details>
*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: sans-serif;
}
body{
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
}

External CSS

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