<span>自定义返回顶部小火箭</span>

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<style>
#back-top {
     position: fixed;
     bottom: 10px;
     right: 5px;
     z-index: 99;
}
#back-top span {
     width: 50px;
     height: 64px;
     display: block;
     background:url(http://images.cnblogs.com/cnblogs_com/seanshao/855033/o_rocket.png) no-repeat center center;
}
#back-top a{outline:none}
</style>
<script type="text/javascript">
$(function() {
	// hide #back-top first
	$("#back-top").hide();
	// fade in #back-top
	$(window).scroll(function() {
		if ($(this).scrollTop() > 500) {
			$('#back-top').fadeIn();
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			$('#back-top').fadeOut();
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	// scroll body to 0px on click
	$('#back-top a').click(function() {
		$('body,html').animate({
			scrollTop: 0
		}, 800);
		return false;
	});
});
</script>
<p id="back-top" style="display:none"><a href="#top"><span></span></a></p>