window.onscroll = function () { //缁戝畾scroll浜嬩欢
      var t = document.documentElement.scrollTop || document.body.scrollTop; //鑾峰彇婊氬姩璺濈
      var h = $(window).height();
      var top_div = document.getElementById("w_grid-1562656070787"); //鏌ヨ骞跺畾涔塪iv鍏冪礌/
      if (t >= 300) { //鍒ゆ柇
          $(top_div).addClass("ztest");
      } else {
          $(top_div).removeClass("ztest");
      }
  };