sticky header missing on tablet size between 768 and 989px

Hi,
I found the following code in this forum to get a sticky header on mobile.

/* Sticky header on mobile */
@media only screen and (max-width: 767px) {
.responsive #top #main {
/* Margin top value should be equal to header height*/
margin-top: 80px;
}
.responsive #top #wrap_all #header {
position: fixed;
}
}

This works only for mobile (and desktop was working anyway). If I change this code to max-width: 989px nothing happens, there is still no sticky header between on screen sizes between 768 and 989px. I need a sticky header on all screen sizes.

Thanks!