Active mainnav with scrolling 500px

Change this line in block mainnav. For t3_blank:

Old:





New:




Custom.css:

@media (min-width:768px) {
.t3-mainnav.affix-top{
position:absolute;
z-index: 1000;
width:100%;
}

.t3-mainnav {
position:relative;
top:-500px;
transition:0.5s ease;
-webkit-transition:0.5s ease;
}
}
.affix {
position: fixed;
top:0;
z-index: 10000;
width:100%!important;
}


How smooth the return of mainnav ?