In this case, you have to change it from js script and you will find it from fixel/templates/ja_fixel/js/script.js file
find and remove it
(function(){
// Add class for mainmenu when scroller
var light = null,
sid = null,
btnnav = $('#fixel-btn-navbar'),
mainnav = $('#t3-mainnav'),
collapsed = btnnav.is(':visible');
if(mainnav.length){
var golight = function() {
if(light != $(window).scrollTop() > mainnav.outerHeight(true) * 0.5){
light = !light;
light ? mainnav.addClass('affix').css('top', Fixel.support.has2d && !collapsed ? -(mainnav.height() +1) : 0) : mainnav.removeClass('light-mainnav').css('top', 0);
//force reflow - fix firefox animation
mainnav[0].offsetWidth;
light ? mainnav.addClass('light-mainnav') : mainnav.removeClass('affix');
}
},
reapply = function(){
collapsed = btnnav.is(':visible');
light ? mainnav.addClass('affix').css('top', Fixel.support.has2d && !collapsed ? -(mainnav.height() +1) : 0) : mainnav.removeClass('light-mainnav').css('top', 0);
};
//bind event
$(window)
.scroll(golight)
.on('resize orientationchange', function(){
clearTimeout(sid);
sid = setTimeout(reapply, 100);
});
}
})();
Let me know if it helps