[j0hnik]

Mansolide,

function addRemoveCSS (){		
			var top = $(document).scrollTop();
			var flag = $(window).width() < 769 && top > 1;

			if(!flag && $('.topblock').css('box-shadow') !== 'none') $('.topblock').css({'box-shadow':'none','background':'rgba(255,255,255,0.0)'});
			if(flag && $('.topblock').css('box-shadow') === 'none') $('.topblock').css({'box-shadow':'0 0 2px rgba(0,0,0,0.5)','background':'rgba(255,255,255,0.9)'});
		}

		$(window).scroll(addRemoveCSS); 
		matchMedia('(min-width: 769px)').addListener(addRemoveCSS);