The following is inserted in the template.css of the "OnePage template":

@media (max-width: 979px) {

sp-header.has-slideshow {

top: 0;

}
}

How can I prevent this. I want "top" to have no value
assigned to it.
So actually:

@media (max-width: 979px) {

sp-header.has-slideshow {

#top: 0;

}
}