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 <div 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 <div class="list">
88 <a href="#" id="avatar" class="avatar" style="float: left;"><img src="http://img.mukewang.com/54447ac70001f5cc00500050.jpg"></a>
89 <div 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/慕课网活动?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.imooc.com/wenda/detail/30394</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/程序员节?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 <div 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 </div>
106 </div>
107 </div>
108 <div 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 </div>
112 </div>
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>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 <div class="box"><img id="image" src="http://img.mukewang.com/54447b06000171a002560191.jpg" width="256" height="191"></div>
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>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 <div id="box" class="box"><img src="http://img.mukewang.com/54447b06000171a002560191.jpg" width="256" height="191"></div>
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>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>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 <div><img src="http://img.mukewang.com/54447f4a0001eb7d01910256.jpg"></div>
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>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://img.mukewang.com/5444835b000100ce00340075.png) 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 <div 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 </div>
43 </body>
44 </html>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://img.mukewang.com/545304730001307300280011.gif); }
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://img.mukewang.com/5453048000015d8800360036.gif); text-indent: -9em; overflow: hidden; }
27 </style>
28 </head>
29
30 <body>
31 <div class="header">
32 <div class="constr">
33 <div 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 </div>
46 </div>
47 </div>
48
49 <div class="main">
50 <div class="constr">
51 <div class="course">
52 <a href="http://www.imooc.com/view/121" class="course-list">
53 <div 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 </div>
58 <h5 class="course-list-h">分享：CSS深入理解之float浮动</h5>
59 <div class="course-list-tips">
60 <span class="l">已完结</span>
61 <span class="r">3514人学习</span>
62 </div>
63 </a>
64 </div>
65 </div>
66 </div>
67 </body>
68 </html>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 > div { 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://img.mukewang.com/545305ba0001f3f600380076.png); 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 <div class="constr">
30 <div class="course-sidebar">
31 <div class="course-sidebar-type"></div>
32 <div 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 </div>
43 </div>
44 </div>
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 datalist
55 result.style.display = "block";
56 }
57 };
58 input.onblur = function() {
59 if (this.value == "") {
60 this.parentNode.className = "course-sidebar-search";
61 }
62 // hide datalist
63 result.style.display = "none";
64 };
65
66 // IE7 that wrap a DIV for avoid bad effect from float
67 if (!document.querySelector) {
68 var div = document.createElement("div");
69 input.parentNode.insertBefore(div, input);
70 div.appendChild(result);
71 }
72 // events of datalist
73 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-IE8
83 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>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://img.mukewang.com/5453076e0001869c01920098.png) 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 <div class="constr">
31 <div class="course-content">
32 <div class="course-list-x">
33 <div class="course-list"></div>
34 <div class="course-list"></div>
35 <div class="course-list"></div>
36 <div class="course-list"></div>
37 <div class="course-list"></div>
38 <div class="course-list"></div>
39 </div>
40 <div class="course-loading-x">
41 <img src="http://img.mukewang.com/5453077400015bba00010001.gif" class="course-loading" alt="加载中...">
42 </div>
43 <div class="course-fixed-x">
44 <div 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 </div>
49 </div>
50 </div>
51 </div>
52 </body>
53 </html>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://img.mukewang.com/5453084a00016ae300120012.gif) 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 <div class="constr">
31 <div class="regist-head">注册</div>
32 <div class="regist-body">
33 <div class="regist-main">
34 <div class="regist-group">
35 <label class="regist-label"><span class="regist-star">*</span>登录邮箱</label>
36 <div 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 </div>
41 </div>
42 <div class="regist-group">
43 <label class="regist-label"><span class="regist-star">*</span>登录密码</label>
44 <div 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 </div>
49 </div>
50 <div class="regist-group">
51 <label class="regist-label"><span class="regist-star">*</span>用户昵称</label>
52 <div class="regist-cell">
53 <input type="password" class="regist-input">
54 </div>
55 </div>
56 <div class="regist-group">
57 <label class="regist-label">手机号码</label>
58 <div class="regist-cell">
59 <input type="tel" class="regist-input">
60 </div>
61 </div>
62 <div class="regist-group">
63 <label class="regist-label"><span class="regist-star">*</span>验 证 码</label>
64 <div class="regist-cell">
65 <input class="regist-input regist-code-input"><img src="http://img.mukewang.com/545308540001678401500040.jpg">
66 </div>
67 </div>
68 <div class="regist-group">
69 <label class="regist-label"> </label>
70 <div 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 </div>
76 </div>
77 </div>
78 </div>
79 </div>
80 </body>
81 </html>五、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！
六、absolute与width和height的关系
1、相互替代性
绝对定位的方向是相互对立的（如：left VS right,top VS bottom）时候，会被拉伸
要想页面全屏显示，可以用position:absolute,width:100%,height:100%或者position:absolute,top:0,bottom:0,
left:0,right:0
2、相互支持性
容器无需固定width/height值，内部元素亦可以拉伸；容器拉伸，内部元素支持百分比width/height值；
demo
无固定width/height容器内的绝对定位元素拉伸
1 <!doctype html>
2 <html>
3 <head>
4 <meta charset="utf-8">
5 <title>无固定width/height容器内的绝对定位元素拉伸</title>
6 <style>
7 body {
8 background-color: #ddd;
9 }
10 img {
11 vertical-align: bottom;
12 }
13 .container {
14 display: inline-block;
15 position: relative;
16 }
17 .cover {
18 position: absolute;
19 left: 0; top: 0; right: 0; bottom: 0;
20 background-color: #fff;
21 opacity: .5; filter: alpha(opacity=50);
22 }
23 </style>
24 </head>
25
26 <body>
27 <span class="container">
28 <i class="cover"></i>
29 <img src="http://img.mukewang.com/547c34cf000171a002560191.jpg" width="512" height="381">
30 </span>
31 <span class="container">
32 <i class="cover"></i>
33 <img src="http://img.mukewang.com/547c34c9000171a002560191.jpg" width="256" height="191">
34 </span>
35 </body>
36 </html>没有宽度和高度声明实现的全屏自适应效果
1 <!doctype html>
2 <html>
3 <head>
4 <meta charset="utf-8">
5 <title>没有宽度和高度声明实现的全屏自适应效果</title>
6 <style>
7 html, body { height: 100%; }
8 .overlay {
9 position: absolute;
10 left: 0; top: 0; right: 0; bottom: 0;
11 background-color: #000;
12 opacity: .5; filter: alpha(opacity=50);
13 }
14 </style>
15 </head>
16
17 <body>
18 <div class="overlay"></div>
19 </body>
20 </html>高度自适应的九宫格效果
1 <!doctype html>
2 <html>
3 <head>
4 <meta charset="utf-8">
5 <title>高度自适应的九宫格效果</title>
6 <style>
7 html, body { height: 100%; margin: 0; }
8 .page {
9 position: absolute;
10 left: 0; top: 0; right: 0; bottom: 0;
11 }
12 .list {
13 float: left;
14 height: 33.3%; width: 33.3%;
15 position: relative;
16 }
17 .list:before {
18 content: '';
19 position: absolute;
20 left: 10px; right: 10px; top: 10px; bottom: 10px;
21 border-radius: 10px;
22 background-color: #cad5eb;
23 }
24 .list:after {
25 content:attr(data-index);
26 position: absolute;
27 height: 30px;
28 left: 0; right: 0; top: 0; bottom: 0;
29 margin: auto;
30 text-align: center;
31 font: 24px/30px bold 'microsoft yahei';
32 }
33 </style>
34 </head>
35
36 <body>
37 <div class="page">
38 <div class="list" data-index="1"></div>
39 <div class="list" data-index="2"></div>
40 <div class="list" data-index="3"></div>
41 <div class="list" data-index="4"></div>
42 <div class="list" data-index="5"></div>
43 <div class="list" data-index="6"></div>
44 <div class="list" data-index="7"></div>
45 <div class="list" data-index="8"></div>
46 <div class="list" data-index="9"></div>
47 </div>
48 </body>
49 </html>left/right拉伸和width同时存在,实现元素水平居中
1 <!doctype html>
2 <html>
3 <head>
4 <meta charset="utf-8">
5 <title>left/right拉伸和width同时存在</title>
6 <style>
7 .image {
8 position: absolute; left: 0; right: 0; width: 50%;
9 }
10 .button {
11 padding-top: 200px;
12 }
13 .button input {
14 width: 280px; height: 40px;
15 font-size: 20px;
16 }
17 </style>
18 </head>
19
20 <body>
21 <img class="image" src="http://img.mukewang.com/547c34c9000171a002560191.jpg" height="191">
22 <p class="button">
23 <input type="button" value="添加margin: auto;" onClick="document.getElementsByTagName('img')[0].style.margin = 'auto';">
24 </p>
25 </body>
26 </html>七、absolute与整体布局
1、html，body{height:100%}
div{position:absolute;left:0;top:0;right:0;bottom:0}实现全屏布局
2、头、尾、侧边栏各居其位
header,footer{position:absolute;left:0;right:0}
header{height:48px;top:0}
footer{height:52px;bottom:0}
aside{width:250px;position:absolute;left:0;top:0;bottom:0}
.content{position:absolute;top:48px;bottom:52px;left:250px;overflow:auto}
效果：
这个时候，头部和尾部都是fix效果，滚动content的时候，只有content区域滚动。避免了移动端position:fixed实现的诸多问题
3.加载效果
参考地址：http://www.imooc.com/learn/192
