Submenu not showing on mobile version?

Question

css

Good afternoon. I have such a problem. Sub-menu or drop-down list, displayed on PC normally.
But on the mobile version under the menu is not displayed. I can not figure out what the problem is and what needs to be registered for this.
https://schoolvoz.net.ua/ Tell me please)

Answer 1

Because that's how it's written

@media only screen and (max-width: 768px)
.main-navigation.toggled-on .sub-menu {
    display: none;
}