Hi to all
Solved By myself. Write here solution so it could be useful for other developer.
In override.css put this :
#gkHeaderNav {
position: absolute;
top: 0;
left: 0;
z-index: 5;
width: 100%;
display: block;
}
#gkHeader.no-header #gkHeaderNav.affix, #gkHeaderNav.affix {
height: auto;
position: fixed;
box-shadow: 0px 6px 6px rgba(0, 0, 0, 0.3);
background-color: #fff;
}
#gkHeaderMod {
margin-top: 200px;
}