Nút scrool back

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$(window).height();var maxheight =
$("body").height();$(function(){$.fn.scrollToMiddle=function(){$(this).hide().removeAttr("href");if($(window).scrollTop()!="maxheight/2-sheight/2"){$(this).fadeIn("slow")}var
 
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<div
 style="bottom: 25px;clip: inherit;position: fixed;right: 5px;"><a
 href="#" id="toTop"><img alt="Đầu trang" border="0"
src="http://r22.imgfast.net/users/2211/12/43/96/album/top10.png"></a><br><a
 href="#" id="toMiddle"><img alt="Giữa trang" border="0"
src="http://r22.imgfast.net/users/2211/12/43/96/album/middle10.png"></a><br><a
 href="#" id="toBottom"><img alt="Cuối trang" border="0"
src="http://r22.imgfast.net/users/2211/12/43/96/album/bottom10.png"></a></div></div>