Use the <details> tag when you want to show extra information only after the visitor clicks on it.
<details>
<summary>Click here to read more</summary>
<p>This text is hidden first. It appears when the visitor clicks.</p>
</details>
Use the <mark> tag when you want to highlight important text.
<p>Learning HTML is <mark>important</mark> when you want to build websites.</p>
