Secondary navigation breakpoint

Hi

I´d like to prevent my secondary navigation menu from collapsing.
I found this css in the forum but it works only over 768px page width. If I set the max-width to 0 or anywhere under 768px it won´t work.

@media (max-width: 800px) {
.secondary-navigation .menu-toggle {
display: block;
}

.secondary-navigation ul,
.secondary-navigation:not(.toggled) .main-nav > ul {
display: none;
}
}

Thank you for your help in advance.

Attila