Overview
<ul class="tree">
<li>
<details open>
<summary>Giant planets</summary>
<ul>
<li>
<details>
<summary>Gas giants</summary>
<ul>
<li>Jupiter</li>
<li>Saturn</li>
</ul>
</details>
</li>
<li>
<details>
<summary>Ice giants</summary>
<ul>
<li>Uranus</li>
<li>Neptune</li>
</ul>
</details>
</li>
</ul>
</details>
</li>
</ul>