Rumah > Artikel > hujung hadapan web > css深入理解之absolute
css深入理解之absolute
- 高洛峰asal
- 2017-02-09 16:30:522008semak imbas
一、absolute和float有相同的特性，包裹性和破坏性
1、absolute和float的相似(看下面的demo，如果图片在左上角，那么用float和absolute都一样)
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <meta name="viewport" content="width=device-width"> 6 <title>absolute和float高尔基</title> 7 <style> 8 body { 9 background-color: #B0DEF5; 10 font-size: 14px; font-family: arial; 11 color: #444; 12 } 13 a { 14 color: #0078b6; 15 text-decoration: none; 16 } 17 a:hover { 18 text-decoration: underline; 19 } 20 em { 21 font-style: normal; 22 color: #aeaeae; 23 margin: 0 5px; 24 } 25 svg { 26 position: absolute; 27 } 28 .container { 29 width: 560px; height: -webkit-calc(100vh - 16px); height: calc(100vh - 16px); 30 margin-left: auto; margin-right: auto; 31 background-color: #fff; 32 } 33 .list { 34 padding: 20px; 35 position: relative; 36 } 37 .space { 38 padding-left: 60px; 39 line-height: 22px; 40 } 41 .space img { 42 vertical-align: text-bottom; 43 } 44 .info { 45 font-size: 12px; 46 overflow: hidden; 47 color: #808080; 48 } 49 .from { 50 float: left; 51 } 52 .from a { 53 color: #9abbc8; 54 } 55 p { 56 margin: 6px 0; 57 } 58 .operate { 59 float: right; 60 } 61 .operate img { 62 vertical-align: text-bottom; 63 margin-right: 3px; 64 } 65 .test { 66 position: relative; 67 font-size: 18px; font-family: 'microsoft yahei'; 68 } 69 .test p { 70 width: 200px; 71 margin-left: auto; margin-right: auto; 72 padding: 5px; 73 background-color: #f0f0f0; 74 } 75 .test input { 76 width: 20px; height: 20px; 77 vertical-align: -4px; 78 } 79 </style> 80 </head> 81 82 <body> 83 <p class="container"> 84 <svg xmlns="http://www.w3.org/2000/svg" width="520" height="360"> 85 <path d="M45 80C45 280,45 320,165 300" stroke-width="1" stroke="#444" fill="none"></path> 86 </svg> 87 <p class="list"> 88 <a href="#" id="avatar" class="avatar" style="float: left;"><img src="http://img.mukewang.com/54447ac70001f5cc00500050.jpg"></a> 89 <p class="space"> 90 <a href="//weibo.com/mukewang" target="_blank" title="慕课网">慕课网</a> 91 <img src="http://img.mukewang.com/54447b1a0001750000160013.png"> 92 <a href="http://huati.weibo.com/k/%E6%85%95%E8%AF%BE%E7%BD%91%E6%B4%BB%E5%8A%A8?from=501">#慕课网活动#</a>【全民晒课ing，火速赢取IT图书】无论你是慕课网的“资深粉丝”，还是刚加入的新同学，在慕课网活动帖：<a href="http://www.imooc.com/wenda/detail/30394">http://www.php.cn/</a> 写下你在慕课网所学习的任意一门课程，并附上课程的学习心得，就有机会赢得精品IT好书。<img src="http://img.mukewang.com/54447cc700010dbf00220022.gif">这事很急哒，仅有2天呦。在<a href="http://huati.weibo.com/k/%E7%A8%8B%E5%BA%8F%E5%91%98%E8%8A%82?from=501">#程序员节#</a>送给自己一份礼物吧！<img src="http://img.mukewang.com/54447af90001ab1c00010001.gif"> 93 <p><img src="http://img.mukewang.com/54447aea0001f43301200084.jpg"></p> 94 <p class="info"> 95 <span class="from"> 96 <a href="#">9月13日 10:27</a> 97 <em>来自</em><a href="#">微博 weibo.com</a> 98 </span> 99 <span class="operate">100 <a href="javascript:" title="赞"><img src="http://img.mukewang.com/54447c350001055b00120013.png">(4)</a><em>|</em>101 <a href="javascript:">转发(5)</a><em>|</em>102 <a href="javascript:">收藏</a><em>|</em>103 <a href="javascript:">评论(2)</a>104 </span>105 </p>106 </p>107 </p>108 <p class="test">109 <p><input type="radio" name="layout" id="float" checked><label for="float">float: left;</label></p>110 <p><input type="radio" name="layout" id="absolute"><label for="absolute">position: absolute;</label></p>111 </p>112 </p>113 <script>114 var eleAvatar = document.getElementById("avatar"),115 eleFloat = document.getElementById("float"),116 eleAbsolute = document.getElementById("absolute");117 118 // SVG路径以及相关动画119 var elePath = document.querySelector("path"), timerPath = null;
120 var funPathMove = function(end) {121 clearTimeout(timerPath);122 var d = elePath.getAttribute("d"), arrD = d.split(" ");123 // 动画起始值124 var start = arrD.slice(-1) * 1;125 if (start == end) return;126 // 速率127 var rate = 5, current = start;128 console.log(arrD);129 var step = function() {130 if (Math.abs(end - current) < 1) {131 current = end;132 } else {133 current += (end - current) / 5;134 timerPath = setTimeout(step, 30);135 }136 // 替换最后一个值137 arrD.splice(-1, 1, current);138 // 曲线走起139 elePath.setAttribute("d", arrD.join(" "));140 };141 step();142 };143 144 if (eleAvatar && eleFloat && eleAbsolute) {145 var attrFloat = eleAvatar.style.cssFloat != undefined? "cssFloat": "styleFloat";146 eleFloat.onclick = function() {147 eleAvatar.style.position = "";148 eleAvatar.style[attrFloat] = "left";149 elePath && funPathMove(300);150 };151 eleAbsolute.onclick = function() {152 eleAvatar.style[attrFloat] = "";153 eleAvatar.style.position = "absolute";154 elePath && funPathMove(340);155 };156 }157 </script>158 </body>159 </html>
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2、破坏性
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <meta name="viewport" content="width=device-width"> 6 <title>absolute的破坏性</title> 7 <style> 8 .box { 9 padding: 10px;10 background-color: #f0f0f0; 11 }12 input {13 position: absolute; top: 234px; 14 width: 160px; height: 32px;15 font-size: 100%;16 }17 </style>18 </head>19 20 <body>21 <p class="box"><img id="image" src="http://img.mukewang.com/54447b06000171a002560191.jpg" width="256" height="191"></p>22 <input id="button" type="button" value="图片absolute化">23 <script>24 var eleImg = document.getElementById("image"), eleBtn = document.getElementById("button");25 if (eleImg != null && eleBtn != null) {26 eleBtn.onclick = function() {27 if (this.absolute) {28 eleImg.style.position = "";29 this.value = "图片absolute化";30 this.absolute = false;31 } else {32 eleImg.style.position = "absolute";33 this.value = "图片去absolute";34 this.absolute = true;35 }36 };37 }38 </script>39 </body>40 </html>
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3、包裹性
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <meta name="viewport" content="width=device-width"> 6 <title>absolute的包裹性</title> 7 <style> 8 .box { 9 padding: 10px;10 background-color: #f0f0f0; 11 }12 input {13 position: absolute; top: 234px; 14 width: 160px; height: 32px;15 font-size: 100%;16 }17 </style>18 </head>19 20 <body>21 <p id="box" class="box"><img src="http://img.mukewang.com/54447b06000171a002560191.jpg" width="256" height="191"></p>22 <input id="button" type="button" value="容器absolute化">23 <script>24 var eleBox = document.getElementById("box"), eleBtn = document.getElementById("button");25 if (eleBox != null && eleBtn != null) {26 eleBtn.onclick = function() {27 if (this.absolute) {28 eleBox.style.position = "";29 this.value = "容器absolute化";30 this.absolute = false;31 } else {32 eleBox.style.position = "absolute";33 this.value = "容器去absolute";34 this.absolute = true;35 }36 };37 }38 </script>39 </body>40 </html>
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二、absolute的独立性
absolute使用的时候，不一定非要和relative在一起，可以独立使用，而且它越独立，能力越大
三、absolute特性
1、去浮动
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <title>折翼天使表现特性一：去浮动</title> 6 <style> 7 input[type=button] { 8 height: 32px; 9 font-size: 100%; 10 }11 </style>12 </head>13 14 <body>15 <img src="http://img.mukewang.com/54447b06000171a002560191.jpg">16 <img src="http://img.mukewang.com/54447f4a0001eb7d01910256.jpg">17 <img src="http://img.mukewang.com/54447f550001ccb002560191.jpg">18 <p><input type="button" id="float" value="点击第2张图片应用float:left"></p>19 <p><input type="button" id="button" value="点击第2张图片应用position:absolute"></p>20 <script>21 var flbtn = document.getElementById("float"),22 button = document.getElementById("button"),23 image2 = document.getElementsByTagName("img")[1];24 if (flbtn && button && image2) {25 var value_init = button.value;26 button.onclick = function() {27 if (this.value == value_init) {28 image2.style.position = "absolute";29 this.value = "撤销";30 } else {31 image2.style.position = "";32 this.value = value_init;33 }34 };35 36 flbtn.onclick = function() {37 image2.style["cssFloat" in this.style? "cssFloat": "styleFloat"] = "left";38 };39 }40 </script>41 </body>42 </html>
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2、位置跟随
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <title>折翼天使表现特性二：位置跟随</title> 6 <style> 7 input[type=button] { 8 height: 32px; 9 font-size: 100%;10 }11 p { margin-left: 260px; }12 img + p { margin-top: 60px; }13 </style>14 </head>15 16 <body>17 <img src="http://img.mukewang.com/54447b06000171a002560191.jpg">18 <p><img src="http://img.mukewang.com/54447f4a0001eb7d01910256.jpg"></p>19 <img src="http://img.mukewang.com/54447f550001ccb002560191.jpg">20 <p><input type="button" id="block" value="点击第2张图片应用display:block"></p>21 <p><input type="button" id="button" value="点击第2张图片应用position:absolute变天使"></p>22 <script>23 var block = document.getElementById("block"),24 button = document.getElementById("button"),25 image2 = document.getElementsByTagName("img")[1];26 if (block && button && image2) {27 var value_init_button = button.value;28 button.onclick = function() {29 if (this.value == value_init_button) {30 image2.style.position = "absolute";31 this.value = "撤销";32 } else {33 image2.style.position = "";34 this.value = value_init_button;35 }36 };37 38 var value_init_block = block.value;39 block.onclick = function() {40 if (this.value == value_init_block) {41 image2.style.display = "block";42 this.value = "撤销";43 } else {44 image2.style.display = "";45 this.value = value_init_block;46 }
47 };48 }49 </script>50 </body>51 </html>
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3.超越overflow
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <title>超越overflow</title> 6 <style> 7 body { 8 background-color: #bbb; 9 }10 .scroll {11 width: 500px; height: 300px;12 margin: 200px auto 0;13 margin-top: -webkit-calc(50vh - 150px);14 margin-top: calc(50vh - 150px);15 border: 1px solid #ccc;16 border-radius: 3px;17 box-shadow: 0 0 3px rgba(0,0,0,.35);18 background-color: #fff;19 overflow: auto;20 }21 .close {22 position: absolute;23 width: 34px; height: 34px; 24 margin: -17px 0 0 483px;25 background: url(http://www.php.cn/) no-repeat;26 }27 .close:hover {28 background-position: 0 -41px; 29 }30 img {31 display: block;32 margin: 10px;33 }34 </style>35 </head>36 37 <body>38 <p class="scroll">39 <a href="javascript:" class="close" title="关闭"></a>40 <img src="http://img.mukewang.com/54447b06000171a002560191.jpg">41 <img src="http://img.mukewang.com/54447f550001ccb002560191.jpg">42 </p>43 </body>44 </html>
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滑动滚动条的时候，关闭按钮不移动，因为设置了absolute
四、absolute实际使用
1、图片图标绝对定位覆盖
上面图片里面的Hot、推荐、vip都是用absolute实现的，而且没有用relative
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <title>图标定位二三事</title> 6 <style> 7 body { font: 14px/1.4 "Microsoft YaHei"; background-color: #EDEFF0; } 8 body, h3, h5 { margin: 0; } 9 img { border: 0 none; vertical-align: bottom; }10 .l { float: left; }.r { float: right; }11 .constr { width: 1200px; margin-left: auto; margin-right: auto; }12 .header { background-color: #2A2C2E; }13 .nav { height: 60px; }14 .nav-list { float: left; font-size: 14px; font-weight: 400; }15 .nav-a { display: inline-block; line-height: 20px; padding: 20px 35px; color: #B5BDC0; text-decoration: none; }16 .nav-a:hover { color: #fff; }17 18 .course { padding-top: 10px; }19 .course-list { float: left; width: 280px; height: 240px; margin: 5px 10px 15px; border-radius: 0 0 1px 1px; background-color: #F7FAF9; background-color: rgba(255,255,255,1); box-shadow: 0 1px 2px #c5c5c5; text-decoration: none; }20 .course-list-img { background-color: #6396F1; }21 .course-list-h { line-height: 50px; font-size: 14px; font-weight: 400; color: #363d40; text-align: center; }22 .course-list-tips { margin: 0 14px; font-size: 12px; color: #b4bbbf; overflow: hidden; }23 24 .icon-hot { position: absolute; width: 28px; height: 11px; margin: -6px 0 0 2px; background: url(http://www.php.cn/); }25 .icon-recom { position: absolute; line-height: 20px; padding: 0 5px; background-color: #f60; color: #fff; font-size: 12px; }26 .icon-vip { position: absolute; width: 36px; height: 36px; margin-left: -36px; background: url(http://www.php.cn/); text-indent: -9em; overflow: hidden; }27 </style>28 </head>29 30 <body>31 <p class="header">32 <p class="constr">33 <p class="nav">34 <h3 class="nav-list">35 <a href="http://www.imooc.com/course/list" class="nav-a">课程</a>36 </h3>37 <h3 class="nav-list">38 <a href="http://www.imooc.com/wenda" class="nav-a">问答</a>39 </h3>40 <h3 class="nav-list">41 <a href="http://www.imooc.com/seek/index" class="nav-a">42 求课<i class="icon-hot"></i>43 </a>44 </h3>45 </p>46 </p>47 </p>48 49 <p class="main">50 <p class="constr">51 <p class="course">52 <a href="http://www.imooc.com/view/121" class="course-list">53 <p class="course-list-img">54 <span class="icon-recom">推荐</span>55 <img width="280" height="160" alt="分享：CSS深入理解之float浮动" src="http://img.mukewang.com/53d74f960001ae9d06000338-300-170.jpg"><!--56 --><i class="icon-vip">vip</i>57 </p>58 <h5 class="course-list-h">分享：CSS深入理解之float浮动</h5>59 <p class="course-list-tips">60 <span class="l">已完结</span>61 <span class="r">3514人学习</span>62 </p>63 </a>64 </p>65 </p>66 </p>67 </body>68 </html>
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2、下拉框定位
用的是无依赖绝对定位，就是只用了absolute，没有用relative
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <title>下拉框定位二三事</title> 6 <style> 7 body { margin: 0; font: 14px/1.4 "Microsoft YaHei"; background-color: #EDEFF0; } 8 .constr { width: 1200px; max-width: 80%; margin-left: auto; margin-right: auto; padding-bottom: 300px; overflow: hidden; } 9 .course-sidebar { width: 262px; float: left; }10 .course-sidebar > p { border: 1px solid #e6e8e9; box-shadow: 0px 1px 2px #d5d7d8; background-color: #fff; }11 .course-sidebar-type { height: 380px; }12 .course-sidebar-search { margin-top: 20px; overflow: hidden; }13 .course-search-input { width: 200px; line-height: 18px; padding: 10px; margin: 0; border: 0 none; font-size: 12px; font-family: inherit; float: left; }14 .course-sidebar-search.focus { border-color: #2ea7e0; }15 .course-search-input:focus { outline: 0 none; }16 .course-search-input::-ms-clear { display: none; }17 .course-search-btn { width: 38px; height: 38px; float: right; background: url(http://www.php.cn/); text-indent: -9em; overflow: hidden; }18 .focus .course-search-btn { background-position: 0 -38px; }19 20 .course-sidebar-result { display: none; position: absolute; width: 260px; margin: 39px 0 0 -1px; padding-left: 0; list-style-type: none; border: 1px solid #e6e8e9; background-color: #fff; box-shadow: 0px 1px 2px #d5d7d8; font-size: 12px; }21 .course-sidebar-result > li { line-height: 30px; padding-left: 12px; }22 .course-sidebar-result > li:hover { background-color: #f9f9f9; }23 .course-sidebar-result a { display: block; color: #5e5e5e; text-decoration: none; }24 .course-sidebar-result a:hover { color: #000; }25 </style>26 </head>27 28 <body>29 <p class="constr">30 <p class="course-sidebar">31 <p class="course-sidebar-type"></p>32 <p class="course-sidebar-search">33 <ul id="result" class="course-sidebar-result">34 <li><a href="http://www.imooc.com/view/121">分享：CSS深入理解之float浮动</a></li>35 <li><a href="http://www.imooc.com/view/118">案例：CSS圆角进化论</a></li>36 <li><a href="http://www.imooc.com/view/93">案例：CSS Sprite雪碧图应用</a></li>37 <li><a href="http://www.imooc.com/view/77">案例：CSS3 3D 特效</a></li>38 <li><a href="http://www.imooc.com/view/57">案例：如何用CSS进行网页布局</a></li>39 </ul>40 <input class="course-search-input" placeholder="课程搜索">41 <a href="javascript:" class="course-search-btn">搜索</a>42 </p>43 </p>44 </p>45 <script>46 (function() {47 var input = document.getElementsByTagName("input")[0],48 result = document.getElementById("result");49 50 if (input && result) {51 input.onfocus = function() {52 this.parentNode.className = "course-sidebar-search focus";53 if (this.value != "") {54 // show datalist55 result.style.display = "block";56 }57 };58 input.onblur = function() {59 if (this.value == "") {60 this.parentNode.className = "course-sidebar-search";61 }62 // hide datalist63 result.style.display = "none";64 };65 66 // IE7 that wrap a p for avoid bad effect from float67 if (!document.querySelector) {68 var p = document.createElement("p");69 input.parentNode.insertBefore(p, input);70 p.appendChild(result);71 }72 // events of datalist73 if ("oninput" in input) {74 input.addEventListener("input", function() {75 if (this.value.trim() != "") {76 result.style.display = "block";77 } else {78 result.style.display = "none";79 }80 });81 } else {82 // IE6-IE883 input.onpropertychange = function(event) {84 event = event || window.event;85 if (event.propertyName == "value" && /focus/.test(this.parentNode.className)) {86 if (this.value != "") {87 result.style.display = "block";88 } else {89 result.style.display = "none";90 }91 }92 }93 }94 }95 96 })();97 </script>98 </body>99 </html>
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3、居中、边缘定位
实现图片居中和边缘定位的一种思路，可以用无限制的absolute，里面用了 和absolute的跟随性，注意代码中的 ，这个很重要
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <title>居中、边缘定位二三事</title> 6 <style> 7 body { margin: 0; font: 14px/1.4 "Microsoft YaHei"; background-color: #EDEFF0; } 8 .constr { width: 1200px; max-width: 80%; margin-left: auto; margin-right: auto; } 9 .course-content { float: right; position: relative; width: 920px; min-height: 1200px; background: #fff; }10 .course-list-x { padding: 20px 10px; overflow: hidden; }11 .course-list { float: left; width: 280px; height: 240px; margin: 5px 10px 15px; border-radius: 0 0 1px 1px; background-color: #F7FAF9; background-color: rgba(255,255,255,1); box-shadow: 0 1px 2px #c5c5c5; text-decoration: none; }12 13 .goto_top_diaocha, .goto_top_app, .goto_top_feed { display: block; width: 48px; height: 48px; margin-top: 10px; background: url(http://www.php.cn/) no-repeat; }14 .goto_top_diaocha { background-position: -48px 0; }15 .goto_top_diaocha:hover { background-position: -48px -50px; }16 .goto_top_app { background-position: -96px 0; }17 .goto_top_app:hover { background-position: -96px -50px; }18 .goto_top_feed { background-position: -144px 0; }19 .goto_top_feed:hover { background-position: -144px -50px; }20 21 .course-loading-x { height: 0; margin-top: 20px; text-align: center; letter-spacing: -.25em; overflow: hidden; }22 .course-loading { position: absolute; margin-left: -26px; }23 24 .course-fixed-x { height: 0; text-align: right; overflow: hidden; }25 .course-fixed { display: inline; position: fixed; margin-left: 20px; bottom: 100px; }26 </style>27 </head>28 29 <body>30 <p class="constr">31 <p class="course-content">32 <p class="course-list-x">33 <p class="course-list"></p>34 <p class="course-list"></p>35 <p class="course-list"></p>36 <p class="course-list"></p>37 <p class="course-list"></p>38 <p class="course-list"></p>39 </p>40 <p class="course-loading-x">41 <img src="http://img.mukewang.com/5453077400015bba00010001.gif" class="course-loading" alt="加载中...">42 </p>43 <p class="course-fixed-x">44 <p class="course-fixed">45 <a href="http://www.imooc.com/activity/diaocha" class="goto_top_diaocha"></a>46 <a href="http://www.imooc.com/mobile/app" class="goto_top_app"></a>47 <a href="http://www.imooc.com/user/feedback" class="goto_top_feed"></a>48 </p>49 </p>50 </p>51 </p>52 </body>53 </html>
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4、文件图片对其与定位
实际项目中，有的地方有星星，有的没有，想要对其文字比较麻烦，就可以用无依赖的absolute
邮箱前面的图标，以及超出框的文字，都可以用无依赖的absolute
它给页面的布局提供了一种新的思路
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <title>文本图标对齐与定位二三事</title> 6 <style> 7 body { margin: 0; font: 14px/1.4 "Microsoft YaHei"; background-color: #EDEFF0; } 8 a { color: #50B6E5; } 9 .constr { width: 1200px; margin-left: auto; margin-right: auto; }10 .regist-head { height: 60px; line-height: 60px; padding-left: 30px; background-color: #be3948; color: #fff; font-size: 18px; }11 .regist-body { min-height: 400px; padding: 100px 0; background-color: #fff; }12 .regist-main { width: 600px; margin-left: auto; margin-right: auto; }13 .regist-group { margin-top: 20px; overflow: hidden; }14 .regist-label { width: 70px; padding-top: 10px; float: left; }15 .regist-cell { display: table-cell; *display: inline-block; }16 .regist-input { height: 18px; line-height: 18px; width: 260px; padding: 10px 5px; margin: 0 10px 0 0; border: 1px solid #d0d6d9; vertical-align: top; }17 .regist-code-input { width: 130px; }18 .regist-btn { display: inline-block; width: 160px; line-height: 40px; background-color: #39b94e; color: #fff; text-align: center; text-decoration: none; }19 .regist-btn:hover { background-color: #33a646; }20 .icon-warn { display: inline-block; width: 20px; height: 21px; background: url(http://www.php.cn/) no-repeat center; }21 22 .regist-star { position: absolute; margin-left: -1em; font-family: simsun; color: #f30; }23 .regist-remark { position: absolute; line-height: 21px; padding-top: 9px; color: #666; }24 .regist-warn { padding-left: 20px; color: #be3948; }25 .regist-warn > .icon-warn { position: absolute; margin-left: -20px; }26 </style>27 </head>28 29 <body>30 <p class="constr">31 <p class="regist-head">注册</p>32 <p class="regist-body">33 <p class="regist-main">34 <p class="regist-group">35 <label class="regist-label"><span class="regist-star">*</span>登录邮箱</label>36 <p class="regist-cell">37 <input type="email" class="regist-input"><span class="regist-remark regist-warn">38 <i class="icon-warn"></i>邮箱格式不准确（演示）39 </span>40 </p>41 </p>42 <p class="regist-group">43 <label class="regist-label"><span class="regist-star">*</span>登录密码</label>44 <p class="regist-cell">45 <input type="password" class="regist-input"><span class="regist-remark">46 请输入6-16位密码，区分大小写，不能使用空格47 </span>48 </p>49 </p>50 <p class="regist-group">51 <label class="regist-label"><span class="regist-star">*</span>用户昵称</label>52 <p class="regist-cell">53 <input type="password" class="regist-input">54 </p>55 </p>56 <p class="regist-group">57 <label class="regist-label">手机号码</label>58 <p class="regist-cell">59 <input type="tel" class="regist-input">60 </p>61 </p>62 <p class="regist-group">63 <label class="regist-label"><span class="regist-star">*</span>验 证 码</label>64 <p class="regist-cell">65 <input class="regist-input regist-code-input"><img src="http://img.mukewang.com/545308540001678401500040.jpg">66 </p>67 </p>68 <p class="regist-group">69 <label class="regist-label"> </label>70 <p class="regist-cell">71 <input type="checkbox" checked><label>我已阅读并同意<a href="##">慕课协议</a>。</label>72 <p>73 <a href="javascript:" class="regist-btn">立即注册</a>74 </p>75 </p>76 </p>77 </p>78 </p>79 </p>80 </body>81 </html>
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四、absolute的脱离文档流
动画尽量作用在absolute上，因为absolute是脱离文档流的，这样动画的时候就不会影响其他元素
z-index无依赖 1.如果只有一个绝对定位元素，自然不需要z-index,自动覆盖普通元素； 2.如果两个绝对定位，控制DOM流的前后顺序达到需要的覆盖效果，依然无z-index； 3.如果多个绝对定位交错，非常非常少见，z-index:1控制； 4.如果非弹窗类的绝对定位元素z-index>2,必定z-index冗余，请优化！
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