When I hover over a menu item with the mouse, several lower modules in Joomla disappear, why is that?

Question

CMS

Good evening. I am a beginner developer. Studied the theory: css, html5, php. Now I've decided to take up the practice. Edited the template. Created a map, carousel. But it is not clear why, when you hover the mouse over the menu, several lower modules disappear. I do not know what to do. What could be the problem and where is it better to dig?
test.vip-photo.com.ua
Thank you.

Answer 1

Select blocks in the developer panel and watch how styles change