I've read this closed Topic:
and I learned that changing this:
<?php wp_list_pages('title_li=0&depth=1'); ?>
<?php wp_list_pages('title_li=0&depth=2'); ?>
will show child pages into my header menu, but not the drop down.
Since my current theme does not natively support menus,
I'd like to understand how to make drop down menus using css.
Many thanks if you could help me.