页面滚动，div的背景图不动；
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<title>演示</title>
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<div class="dcent" style="background-color: wheat;">洛神赋</div>
<div class="dcent" style="background-color: lightgoldenrodyellow;">黄初三年，余朝京师，还济洛川。古人有言，斯水之神，名曰宓妃。感宋玉对楚王神女之事，遂作斯赋。其辞曰：</div>
<div class="dcent" style="background-color: powderblue;">洛神赋</div>
<div style="margin: 0 auto;height: 100%;width: 100%;font-size: 14px;background: #fff;overflow: visible;display: block;line-height: 1.5;">
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<h3 class="dsh">余从京域，言归东藩。</h3>
<h6 class="dsh6">背伊阙，越轘辕，经通谷，陵景山。日既西倾，车殆马烦。尔乃税驾乎蘅皋，秣驷乎芝田，容与乎阳林，流眄乎洛川。</h6>
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<p style="height: 500px;width: 80%;font-size: 20px;margin: 0 auto;color: #fff">于是精移神骇，忽焉思散。俯则未察，仰以殊观，睹一丽人，于岩之畔。乃援御者而告之曰：“尔有觌于彼者乎？彼何人斯？若此之艳也！”御者对曰：“臣闻河洛之神，名曰宓妃。然则君王所见，无乃是乎？其状若何？臣愿闻之。”</p>
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<p class="secp">余告之曰：“其形也，翩若惊鸿，婉若游龙。荣曜秋菊，华茂春松。髣髴兮若轻云之蔽月，飘飖兮若流风之回雪。远而望之，皎若太阳升朝霞；</p>
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<h3 class="dsh">迫而察之，灼若芙蕖出渌波。</h3>
<p class="secp">秾纤得衷，修短合度。肩若削成，腰如约素。延颈秀项，皓质呈露。芳泽无加，铅华弗御。云髻峨峨，修眉联娟。丹唇外朗，皓齿内鲜，明眸善睐，靥辅承权。</p>
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<section style="background-color: #f6f6f6 !important;background-image: url(./bg_2.jpg);background-repeat: no-repeat;background-size: cover;background-attachment: fixed;">
<h3 class="dsh">瑰姿艳逸，仪静体闲。柔情绰态，媚于语言。</h3>
<h6 class="dsh6">奇服旷世，骨像应图。披罗衣之璀粲兮，珥瑶碧之华琚。戴金翠之首饰，缀明珠以耀躯。践远游之文履，曳雾绡之轻裾。微幽兰之芳蔼兮，步踟蹰于山隅。于是忽焉纵体，以遨以嬉。</h6>
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<p class="secp">左倚采旄，右荫桂旗。壤皓腕于神浒兮，采湍濑之玄芝。余情悦其淑美兮，心振荡而不怡。无良媒以接欢兮，托微波而通辞。</p>
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<h3 class="dsh">鬼刀漫画</h3>
<p class="secp">愿诚素之先达兮，解玉佩以要之。嗟佳人之信修兮，羌习礼而明诗。抗琼珶以和予兮，指潜渊而为期。执眷眷之款实兮，惧斯灵之我欺。感交甫之弃言兮，怅犹豫而狐疑。收和颜而静志兮，申礼防以自持。</p>
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<section style="background-color: #f6f6f6 !important;background-image: url(./bg_3.jpg);background-repeat: no-repeat;background-size: cover;background-attachment: fixed;">
<h3 class="dsh">于是洛灵感焉，徙倚彷徨，神光离合，乍阴乍阳。竦轻躯以鹤立，若将飞而未翔。</h3>
<h6 class="dsh6">践椒涂之郁烈，步蘅薄而流芳。超长吟以永慕兮，声哀厉而弥长。尔乃众灵杂遝，命俦啸侣，或戏清流，或翔神渚，或采明珠，或拾翠羽。</h6>
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<p style="height: 500px;width: 100%">从南湘之二妃，携汉滨之游女。叹匏瓜之无匹兮，咏牵牛之独处。扬轻袿之猗靡兮，翳修袖以延伫。体迅飞凫，飘忽若神，陵波微步，罗袜生尘。动无常则，若危若安。</p>
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<p class="secp">进止难期，若往若还。转眄流精，光润玉颜。含辞未吐，气若幽兰。华容婀娜，令我忘餐。于是屏翳收风，川后静波。冯夷鸣鼓，女娲清歌。腾文鱼以警乘，鸣玉鸾以偕逝。六龙俨其齐首，载云车之容裔。鲸鲵踊而夹毂，水禽翔而为卫。于是越北沚，过南冈，纡素领，回清阳，动朱唇以徐言，陈交接之大纲。恨人神之道殊兮，怨盛年之莫当。抗罗袂以掩涕兮，泪流襟之浪浪。悼良会之永绝兮，哀一逝而异乡。无微情以效爱兮，献江南之明珰。虽潜处于太阴，长寄心于君王。忽不悟其所舍，怅神宵而蔽光。</p>
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<div class="dcent" style="background-color: powderblue;">于是背下陵高，足往神留，遗情想像，顾望怀愁。冀灵体之复形，御轻舟而上溯。浮长川而忘返，思绵绵而增慕。</div>
<div class="dcent" style="background-color: white;">夜耿耿而不寐，沾繁霜而至曙。命仆夫而就驾，吾将归乎东路。揽騑辔以抗策，怅盘桓而不能去。</div>
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