How to write a multi-level associated drop-down list, as shown below_html/css_WEB-ITnose

As the title, the effect is as shown below

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As the title, come to me quickly

This There are a lot of effects on the Internet, you can look for them. In fact, it is a question of hierarchical control: which layer is displayed and which layer is hidden. Find the relationship between the selector and it will be easy