$(function(){



 var shrinkHeader = 150;


  $(window).scroll(function() {
    var scroll = getCurrentScroll();
      if ( scroll >= shrinkHeader ) {
           $('.main-header').addClass('shrink');
        }
        else {
            $('.main-header').removeClass('shrink');
        }
  });


function getCurrentScroll() {
    return window.pageYOffset;
    }


});