jQuery.fn.isOnScreen = function(){
 var win = jQuery(window);
 var viewport = {
  top : win.scrollTop(),
  left : win.scrollLeft()
 };
 viewport.right = viewport.left + win.width();
 viewport.bottom = viewport.top + win.height();
 var bounds = this.offset();
 bounds.right = bounds.left + this.outerWidth();
 bounds.bottom = bounds.top + this.outerHeight();
 return (!(viewport.right < bounds.left || viewport.left > bounds.right || viewport.bottom < bounds.top || viewport.top > bounds.bottom));
};



jQuery(window).scroll(function() {
        if(!jQuery('#section_one').isOnScreen()){
            $('#header-logo').height(0);
            $('#header-menu').height(60).width(60);
            $('header').css("background-color", "rgb(41, 41, 41, 0.2)");
        }else{
            $('#header-logo').height(204)
            $('#header-menu').height(50).width(50);
            $('header').css("background-color", "rgb(41, 41, 41, 1)");
        }
});