W3.CSS menu pointing to multiple pages?

[JanCH]

I'm editing this template:

https://www.w3schools.com/w3css/tryw3css_templates_clothing_store.htm

All the links in the left menu point to the same page, like this:

<a href="#" class="w3-bar-item w3-button">Dresses</a>

However, when I try to point to a new page, like this:

<a href="w3test01.html" class="w3-bar-item w3-button">Test</a>

then the new page covers the menu as well.

How can I make new pages appear behind the menu, like the original page?

All the W3.CSS templates only use one page.

Thanks for any help!