css之absolute

时间：2023-03-09 23:19:22
css之absolute

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)

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <meta name="viewport" content="width=device-width">

 <title>absolute和float高尔基</title>

 <style>

 body {

     background-color: #B0DEF5;

     font-size: 14px; font-family: arial;

     color: #444;

 }

 a {

     color: #0078b6;

     text-decoration: none;

 }

 a:hover {

     text-decoration: underline;

 }

 em {

     font-style: normal;

     color: #aeaeae;

     margin: 0 5px;

 }

 svg {

     position: absolute;

 }

 .container {

     width: 560px; height: -webkit-calc(100vh - 16px); height: calc(100vh - 16px);

     margin-left: auto; margin-right: auto;

     background-color: #fff;

 }

 .list {

     padding: 20px;

     position: relative;

 }

 .space {

     padding-left: 60px;

     line-height: 22px;

 }

 .space img {

     vertical-align: text-bottom;

 }

 .info {

     font-size: 12px;

     overflow: hidden;

     color: #808080;

 }

 .from {

     float: left;

 }

 .from a {

     color: #9abbc8;

 }

 p {

     margin: 6px 0;

 }

 .operate {

     float: right;

 }

 .operate img {

     vertical-align: text-bottom;

     margin-right: 3px;

 }

 .test {

     position: relative;

     font-size: 18px; font-family: 'microsoft yahei';

 }

 .test p {

    width: 200px;

    margin-left: auto; margin-right: auto;

    padding: 5px;

    background-color: #f0f0f0;

 }

 .test input {

     width: 20px; height: 20px;

     vertical-align: -4px;

 }

 </style>

 </head>

 <body>

 <div class="container">

     <svg xmlns="http://www.w3.org/2000/svg" width="520" height="360">

         <path d="M45 80C45 280,45 320,165 300" stroke-width="1" stroke="#444" fill="none"></path>

     </svg>

     <div class="list">

         <a href="#" id="avatar" class="avatar" style="float: left;"><img src="http://img.mukewang.com/54447ac70001f5cc00500050.jpg"></a>

         <div class="space">

             <a href="//weibo.com/mukewang" target="_blank" title="慕课网">慕课网</a>

             <img src="http://img.mukewang.com/54447b1a0001750000160013.png">

             <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.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/%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">

             <p><img src="http://img.mukewang.com/54447aea0001f43301200084.jpg"></p>

             <div class="info">

                    <span class="from">

                     <a href="#">9月13日 10:27</a>

                     <em>来自</em><a href="#">微博 weibo.com</a>

                 </span>

                 <span class="operate">

                     <a href="javascript:" title="赞"><img src="http://img.mukewang.com/54447c350001055b00120013.png">(4)</a><em>|</em>

                     <a href="javascript:">转发(5)</a><em>|</em>

                     <a href="javascript:">收藏</a><em>|</em>

                     <a href="javascript:">评论(2)</a>

                 </span>

             </div>

         </div>

     </div>

     <div class="test">

         <p><input type="radio" name="layout" id="float" checked><label for="float">float: left;</label></p>

         <p><input type="radio" name="layout" id="absolute"><label for="absolute">position: absolute;</label></p>

     </div>

 </div>

 <script>

 var eleAvatar = document.getElementById("avatar"),

     eleFloat = document.getElementById("float"),

     eleAbsolute = document.getElementById("absolute");

 // SVG路径以及相关动画

 var elePath = document.querySelector("path"), timerPath = null;

 var funPathMove = function(end) {

     clearTimeout(timerPath);

     var d = elePath.getAttribute("d"), arrD = d.split(" ");

     // 动画起始值

     var start = arrD.slice(-1) * 1;

     if (start == end) return;

     // 速率

     var rate = 5, current = start;

     console.log(arrD);

     var step = function() {

         if (Math.abs(end - current) < 1) {

             current = end;

         } else {

             current += (end - current) / 5;

             timerPath = setTimeout(step, 30);

         }

         // 替换最后一个值

         arrD.splice(-1, 1, current);

         // 曲线走起

         elePath.setAttribute("d", arrD.join(" "));

     };

     step();

 };

 if (eleAvatar && eleFloat && eleAbsolute) {

     var attrFloat = eleAvatar.style.cssFloat != undefined? "cssFloat": "styleFloat";

     eleFloat.onclick = function() {

         eleAvatar.style.position = "";

         eleAvatar.style[attrFloat] = "left";

         elePath && funPathMove(300);

     };

     eleAbsolute.onclick = function() {

         eleAvatar.style[attrFloat] = "";

         eleAvatar.style.position = "absolute";

         elePath && funPathMove(340);

     };

 }

 </script>

 </body>

 </html>

2、破坏性

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <meta name="viewport" content="width=device-width">

 <title>absolute的破坏性</title>

 <style>

 .box {

     padding: 10px;

     background-color: #f0f0f0;

 }

 input {

     position: absolute; top: 234px;

     width: 160px; height: 32px;

     font-size: 100%;

 }

 </style>

 </head>

 <body>

 <div class="box"><img id="image" src="http://img.mukewang.com/54447b06000171a002560191.jpg" width="256" height="191"></div>

 <input id="button" type="button" value="图片absolute化">

 <script>

 var eleImg = document.getElementById("image"), eleBtn = document.getElementById("button");

 if (eleImg != null && eleBtn != null) {

     eleBtn.onclick = function() {

         if (this.absolute) {

             eleImg.style.position = "";

             this.value = "图片absolute化";

             this.absolute = false;

         } else {

             eleImg.style.position = "absolute";

             this.value = "图片去absolute";

             this.absolute = true;

         }

     };

 }

 </script>

 </body>

 </html>

3、包裹性

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <meta name="viewport" content="width=device-width">

 <title>absolute的包裹性</title>

 <style>

 .box {

     padding: 10px;

     background-color: #f0f0f0;

 }

 input {

     position: absolute; top: 234px;

     width: 160px; height: 32px;

     font-size: 100%;

 }

 </style>

 </head>

 <body>

 <div id="box" class="box"><img src="http://img.mukewang.com/54447b06000171a002560191.jpg" width="256" height="191"></div>

 <input id="button" type="button" value="容器absolute化">

 <script>

 var eleBox = document.getElementById("box"), eleBtn = document.getElementById("button");

 if (eleBox != null && eleBtn != null) {

     eleBtn.onclick = function() {

         if (this.absolute) {

             eleBox.style.position = "";

             this.value = "容器absolute化";

             this.absolute = false;

         } else {

             eleBox.style.position = "absolute";

             this.value = "容器去absolute";

             this.absolute = true;

         }

     };

 }

 </script>

 </body>

 </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

css之absolute

三、absolute特性

1、去浮动

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>折翼天使表现特性一：去浮动</title>

 <style>

 input[type=button] {

     height: 32px;

     font-size: 100%;

 }

 </style>

 </head>

 <body>

 <img src="http://img.mukewang.com/54447b06000171a002560191.jpg">

 <img src="http://img.mukewang.com/54447f4a0001eb7d01910256.jpg">

 <img src="http://img.mukewang.com/54447f550001ccb002560191.jpg">

 <p><input type="button" id="float" value="点击第2张图片应用float:left"></p>

 <p><input type="button" id="button" value="点击第2张图片应用position:absolute"></p>

 <script>

 var flbtn = document.getElementById("float"),

     button = document.getElementById("button"),

     image2 = document.getElementsByTagName("img")[1];

 if (flbtn && button && image2) {

     var value_init = button.value;

     button.onclick = function() {

         if (this.value == value_init) {

             image2.style.position = "absolute";

             this.value = "撤销";

         } else {

             image2.style.position = "";

             this.value = value_init;

         }

     };

     flbtn.onclick = function() {

         image2.style["cssFloat" in this.style? "cssFloat": "styleFloat"] = "left";

     };

 }

 </script>

 </body>

 </html>

2、位置跟随

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>折翼天使表现特性二：位置跟随</title>

 <style>

 input[type=button] {

     height: 32px;

     font-size: 100%;

 }

 p { margin-left: 260px; }

 img + p { margin-top: 60px; }

 </style>

 </head>

 <body>

 <img src="http://img.mukewang.com/54447b06000171a002560191.jpg">

 <div><img src="http://img.mukewang.com/54447f4a0001eb7d01910256.jpg"></div>

 <img src="http://img.mukewang.com/54447f550001ccb002560191.jpg">

 <p><input type="button" id="block" value="点击第2张图片应用display:block"></p>

 <p><input type="button" id="button" value="点击第2张图片应用position:absolute变天使"></p>

 <script>

 var block = document.getElementById("block"),

     button = document.getElementById("button"),

     image2 = document.getElementsByTagName("img")[1];

 if (block && button && image2) {

     var value_init_button = button.value;

     button.onclick = function() {

         if (this.value == value_init_button) {

             image2.style.position = "absolute";

             this.value = "撤销";

         } else {

             image2.style.position = "";

             this.value = value_init_button;

         }

     };

     var value_init_block = block.value;

     block.onclick = function() {

         if (this.value == value_init_block) {

             image2.style.display = "block";

             this.value = "撤销";

         } else {

             image2.style.display = "";

             this.value = value_init_block;

         }

     };

 }

 </script>

 </body>

 </html>

3.超越overflow

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>超越overflow</title>

 <style>

 body {

     background-color: #bbb;

 }

 .scroll {

     width: 500px; height: 300px;

     margin: 200px auto 0;

     margin-top: -webkit-calc(50vh - 150px);

     margin-top: calc(50vh - 150px);

     border: 1px solid #ccc;

     border-radius: 3px;

     box-shadow: 0 0 3px rgba(0,0,0,.35);

     background-color: #fff;

     overflow: auto;

 }

 .close {

     position: absolute;

     width: 34px; height: 34px;

     margin: -17px 0 0 483px;

     background: url(http://img.mukewang.com/5444835b000100ce00340075.png) no-repeat;

 }

 .close:hover {

     background-position: 0 -41px;

 }

 img {

     display: block;

     margin: 10px;

 }

 </style>

 </head>

 <body>

 <div class="scroll">

     <a href="javascript:" class="close" title="关闭"></a>

     <img src="http://img.mukewang.com/54447b06000171a002560191.jpg">

     <img src="http://img.mukewang.com/54447f550001ccb002560191.jpg">

 </div>

 </body>

 </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

css之absolute

上面图片里面的Hot、推荐、vip都是用absolute实现的，而且没有用relative

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>图标定位二三事</title>

 <style>

 body { font: 14px/1.4 "Microsoft YaHei"; background-color: #EDEFF0; }

 body, h3, h5 { margin: 0; }

 img { border: 0 none; vertical-align: bottom; }

 .l { float: left; }.r { float: right; }

 .constr { width: 1200px; margin-left: auto; margin-right: auto; }

 .header { background-color: #2A2C2E; }

 .nav { height: 60px; }

 .nav-list { float: left; font-size: 14px; font-weight: 400; }

 .nav-a { display: inline-block; line-height: 20px; padding: 20px 35px; color: #B5BDC0; text-decoration: none; }

 .nav-a:hover { color: #fff; }

 .course { padding-top: 10px; }

 .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; }

 .course-list-img { background-color: #6396F1; }

 .course-list-h { line-height: 50px; font-size: 14px; font-weight: 400; color: #363d40; text-align: center; }

 .course-list-tips { margin: 0 14px; font-size: 12px; color: #b4bbbf; overflow: hidden; }

 .icon-hot { position: absolute; width: 28px; height: 11px; margin: -6px 0 0 2px; background: url(http://img.mukewang.com/545304730001307300280011.gif); }

 .icon-recom { position: absolute; line-height: 20px; padding: 0 5px; background-color: #f60; color: #fff; font-size: 12px; }

 .icon-vip { position: absolute; width: 36px; height: 36px; margin-left: -36px; background: url(http://img.mukewang.com/5453048000015d8800360036.gif); text-indent: -9em; overflow: hidden; }

 </style>

 </head>

 <body>

 <div class="header">

     <div class="constr">

         <div class="nav">

             <h3 class="nav-list">

                 <a href="http://www.imooc.com/course/list" class="nav-a">课程</a>

             </h3>

             <h3 class="nav-list">

                 <a href="http://www.imooc.com/wenda" class="nav-a">问答</a>

             </h3>

             <h3 class="nav-list">

                 <a href="http://www.imooc.com/seek/index" class="nav-a">

                     求课<i class="icon-hot"></i>

                 </a>

             </h3>

         </div>

     </div>

 </div>

 <div class="main">

     <div class="constr">

         <div class="course">

             <a href="http://www.imooc.com/view/121" class="course-list">

                 <div class="course-list-img">

                     <span class="icon-recom">推荐</span>

                     <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"><!--

                     --><i class="icon-vip">vip</i>

                 </div>

                 <h5 class="course-list-h">分享：CSS深入理解之float浮动</h5>

                 <div class="course-list-tips">

                     <span class="l">已完结</span>

                     <span class="r">3514人学习</span>

                 </div>

             </a>

         </div>

     </div>

 </div>

 </body>

 </html>

2、下拉框定位

css之absolute

用的是无依赖绝对定位，就是只用了absolute，没有用relative

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>下拉框定位二三事</title>

 <style>

 body { margin: 0; font: 14px/1.4 "Microsoft YaHei"; background-color: #EDEFF0; }

 .constr { width: 1200px; max-width: 80%; margin-left: auto; margin-right: auto; padding-bottom: 300px; overflow: hidden; }

 .course-sidebar { width: 262px; float: left; }

 .course-sidebar > div { border: 1px solid #e6e8e9; box-shadow: 0px 1px 2px #d5d7d8; background-color: #fff; }

 .course-sidebar-type { height: 380px; }

 .course-sidebar-search { margin-top: 20px; overflow: hidden; }

 .course-search-input { width: 200px; line-height: 18px; padding: 10px; margin: 0; border: 0 none; font-size: 12px; font-family: inherit; float: left; }

 .course-sidebar-search.focus { border-color: #2ea7e0; }

 .course-search-input:focus { outline: 0 none; }

 .course-search-input::-ms-clear { display: none; }

 .course-search-btn { width: 38px; height: 38px; float: right; background: url(http://img.mukewang.com/545305ba0001f3f600380076.png); text-indent: -9em; overflow: hidden; }

 .focus .course-search-btn { background-position: 0 -38px; }

 .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; }

 .course-sidebar-result > li { line-height: 30px; padding-left: 12px; }

 .course-sidebar-result > li:hover { background-color: #f9f9f9; }

 .course-sidebar-result a { display: block; color: #5e5e5e; text-decoration: none; }

 .course-sidebar-result a:hover { color: #000; }

 </style>

 </head>

 <body>

 <div class="constr">

     <div class="course-sidebar">

         <div class="course-sidebar-type"></div>

         <div class="course-sidebar-search">

             <ul id="result" class="course-sidebar-result">

                 <li><a href="http://www.imooc.com/view/121">分享：CSS深入理解之float浮动</a></li>

                 <li><a href="http://www.imooc.com/view/118">案例：CSS圆角进化论</a></li>

                 <li><a href="http://www.imooc.com/view/93">案例：CSS Sprite雪碧图应用</a></li>

                 <li><a href="http://www.imooc.com/view/77">案例：CSS3 3D 特效</a></li>

                 <li><a href="http://www.imooc.com/view/57">案例：如何用CSS进行网页布局</a></li>

             </ul>

             <input class="course-search-input" placeholder="课程搜索">

             <a href="javascript:" class="course-search-btn">搜索</a>

         </div>

     </div>

 </div>

 <script>

 (function() {

     var input = document.getElementsByTagName("input")[0],

         result = document.getElementById("result");

     if (input && result) {

         input.onfocus = function() {

             this.parentNode.className = "course-sidebar-search focus";

             if (this.value != "") {

                 // show datalist

                 result.style.display = "block";

             }

         };

         input.onblur = function() {

             if (this.value == "") {

                 this.parentNode.className = "course-sidebar-search";

             }

             // hide datalist

             result.style.display = "none";

         };

         // IE7 that wrap a DIV for avoid bad effect from float

         if (!document.querySelector) {

             var div = document.createElement("div");

             input.parentNode.insertBefore(div, input);

             div.appendChild(result);

         }

         // events of datalist

         if ("oninput" in input) {

             input.addEventListener("input", function() {

                 if (this.value.trim() != "") {

                     result.style.display = "block";

                 } else {

                     result.style.display = "none";

                 }

             });

         } else {

             // IE6-IE8

             input.onpropertychange = function(event) {

                 event = event || window.event;

                 if (event.propertyName == "value" && /focus/.test(this.parentNode.className)) {

                     if (this.value != "") {

                         result.style.display = "block";

                     } else {

                         result.style.display = "none";

                     }

                 }

             }

         }

     }

 })();

 </script>

 </body>

 </html>

3、居中、边缘定位

css之absolute

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&nbsp;和absolute的跟随性，注意代码中的&nbsp;，这个很重要

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>居中、边缘定位二三事</title>

 <style>

 body { margin: 0; font: 14px/1.4 "Microsoft YaHei"; background-color: #EDEFF0; }

 .constr { width: 1200px; max-width: 80%; margin-left: auto; margin-right: auto; }

 .course-content { float: right; position: relative; width: 920px; min-height: 1200px; background: #fff; }

 .course-list-x { padding: 20px 10px; overflow: hidden; }

 .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; }

 .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; }

 .goto_top_diaocha { background-position: -48px 0; }

 .goto_top_diaocha:hover { background-position: -48px -50px; }

 .goto_top_app { background-position: -96px 0; }

 .goto_top_app:hover { background-position: -96px -50px; }

 .goto_top_feed { background-position: -144px 0; }

 .goto_top_feed:hover { background-position: -144px -50px; }

 .course-loading-x { height: 0; margin-top: 20px; text-align: center; letter-spacing: -.25em; overflow: hidden; }

 .course-loading { position: absolute; margin-left: -26px; }

 .course-fixed-x { height: 0; text-align: right; overflow: hidden; }

 .course-fixed { display: inline; position: fixed; margin-left: 20px; bottom: 100px; }

 </style>

 </head>

 <body>

 <div class="constr">

     <div class="course-content">

         <div class="course-list-x">

             <div class="course-list"></div>

             <div class="course-list"></div>

             <div class="course-list"></div>

             <div class="course-list"></div>

             <div class="course-list"></div>

             <div class="course-list"></div>

         </div>

         <div class="course-loading-x">

             &nbsp;<img src="http://img.mukewang.com/5453077400015bba00010001.gif" class="course-loading" alt="加载中...">

         </div>

         <div class="course-fixed-x">

             &nbsp;<div class="course-fixed">

                 <a href="http://www.imooc.com/activity/diaocha" class="goto_top_diaocha"></a>

                 <a href="http://www.imooc.com/mobile/app" class="goto_top_app"></a>

                 <a href="http://www.imooc.com/user/feedback" class="goto_top_feed"></a>

             </div>

         </div>

     </div>

 </div>

 </body>

 </html>

4、文件图片对其与定位

css之absolute

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

 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>文本图标对齐与定位二三事</title>

 <style>

 body { margin: 0; font: 14px/1.4 "Microsoft YaHei"; background-color: #EDEFF0; }

 a { color: #50B6E5; }

 .constr { width: 1200px; margin-left: auto; margin-right: auto; }

 .regist-head { height: 60px; line-height: 60px; padding-left: 30px; background-color: #be3948; color: #fff; font-size: 18px; }

 .regist-body { min-height: 400px; padding: 100px 0; background-color: #fff; }

 .regist-main { width: 600px; margin-left: auto; margin-right: auto; }

 .regist-group { margin-top: 20px; overflow: hidden; }

 .regist-label { width: 70px; padding-top: 10px; float: left; }

 .regist-cell { display: table-cell; *display: inline-block; }

 .regist-input { height: 18px; line-height: 18px; width: 260px; padding: 10px 5px; margin: 0 10px 0 0; border: 1px solid #d0d6d9; vertical-align: top; }

 .regist-code-input { width: 130px; }

 .regist-btn { display: inline-block; width: 160px; line-height: 40px; background-color: #39b94e; color: #fff; text-align: center; text-decoration: none; }

 .regist-btn:hover { background-color: #33a646; }

 .icon-warn { display: inline-block; width: 20px; height: 21px; background: url(http://img.mukewang.com/5453084a00016ae300120012.gif) no-repeat center; }

 .regist-star { position: absolute; margin-left: -1em; font-family: simsun; color: #f30; }

 .regist-remark { position: absolute; line-height: 21px; padding-top: 9px; color: #666; }

 .regist-warn { padding-left: 20px; color: #be3948; }

 .regist-warn > .icon-warn { position: absolute; margin-left: -20px; }

 </style>

 </head>

 <body>

 <div class="constr">

     <div class="regist-head">注册</div>

     <div class="regist-body">

         <div class="regist-main">

             <div class="regist-group">

                 <label class="regist-label"><span class="regist-star">*</span>登录邮箱</label>

                 <div class="regist-cell">

                     <input type="email" class="regist-input"><span class="regist-remark regist-warn">

                         <i class="icon-warn"></i>邮箱格式不准确（演示）

                     </span>

                 </div>

             </div>

             <div class="regist-group">

                 <label class="regist-label"><span class="regist-star">*</span>登录密码</label>

                 <div class="regist-cell">

                     <input type="password" class="regist-input"><span class="regist-remark">

                         请输入6-16位密码，区分大小写，不能使用空格

                     </span>

                 </div>

             </div>

             <div class="regist-group">

                 <label class="regist-label"><span class="regist-star">*</span>用户昵称</label>

                 <div class="regist-cell">

                     <input type="password" class="regist-input">

                 </div>

             </div>

             <div class="regist-group">

                 <label class="regist-label">手机号码</label>

                 <div class="regist-cell">

                     <input type="tel" class="regist-input">

                 </div>

             </div>

             <div class="regist-group">

                 <label class="regist-label"><span class="regist-star">*</span>验 证 码</label>

                 <div class="regist-cell">

                     <input class="regist-input regist-code-input"><img src="http://img.mukewang.com/545308540001678401500040.jpg">

                 </div>

             </div>

             <div class="regist-group">

                 <label class="regist-label">&nbsp;</label>

                 <div class="regist-cell">

                     <input type="checkbox" checked><label>我已阅读并同意<a href="##">慕课协议</a>。</label>

                     <p>

                         <a href="javascript:" class="regist-btn">立即注册</a>

                     </p>

                 </div>

             </div>

         </div>

     </div>

 </div>

 </body>

 </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







 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>无固定width/height容器内的绝对定位元素拉伸</title>

 <style>

 body {

     background-color: #ddd;

 }

 img {

     vertical-align: bottom;

 }

 .container {

     display: inline-block;

     position: relative;

 }

 .cover {

     position: absolute;

     left: 0; top: 0; right: 0; bottom: 0;

     background-color: #fff;

     opacity: .5; filter: alpha(opacity=50);

 }

 </style>

 </head>

 <body>

 <span class="container">

     <i class="cover"></i>

     <img src="http://img.mukewang.com/547c34cf000171a002560191.jpg" width="512" height="381">

 </span>

 <span class="container">

     <i class="cover"></i>

     <img src="http://img.mukewang.com/547c34c9000171a002560191.jpg" width="256" height="191">

 </span>

 </body>

 </html>








没有宽度和高度声明实现的全屏自适应效果






 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>没有宽度和高度声明实现的全屏自适应效果</title>

 <style>

 html, body { height: 100%; }

 .overlay {

     position: absolute;

     left: 0; top: 0; right: 0; bottom: 0;

     background-color: #000;

     opacity: .5; filter: alpha(opacity=50);

 }

 </style>

 </head>

 <body>

 <div class="overlay"></div>

 </body>

 </html>






高度自适应的九宫格效果






 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>高度自适应的九宫格效果</title>

 <style>

 html, body { height: 100%; margin: 0; }

 .page {

     position: absolute;

     left: 0; top: 0; right: 0; bottom: 0;

 }

 .list {

     float: left;

     height: 33.3%; width: 33.3%;

     position: relative;

 }

 .list:before {

     content: '';

     position: absolute;

     left: 10px; right: 10px; top: 10px; bottom: 10px;

     border-radius: 10px;

     background-color: #cad5eb;

 }

 .list:after {

     content:attr(data-index);

     position: absolute;

     height: 30px;

     left: 0; right: 0; top: 0; bottom: 0;

     margin: auto;

     text-align: center;

     font: 24px/30px bold 'microsoft yahei';

 }

 </style>

 </head>

 <body>

 <div class="page">

     <div class="list" data-index="1"></div>

     <div class="list" data-index="2"></div>

     <div class="list" data-index="3"></div>

     <div class="list" data-index="4"></div>

     <div class="list" data-index="5"></div>

     <div class="list" data-index="6"></div>

     <div class="list" data-index="7"></div>

     <div class="list" data-index="8"></div>

     <div class="list" data-index="9"></div>

 </div>

 </body>

 </html>






left/right拉伸和width同时存在,实现元素水平居中






 <!doctype html>

 <html>

 <head>

 <meta charset="utf-8">

 <title>left/right拉伸和width同时存在</title>

 <style>

 .image {

     position: absolute; left: 0; right: 0; width: 50%;

 }

 .button {

     padding-top: 200px;

 }

 .button input {

     width: 280px; height: 40px;

     font-size: 20px;

 }

 </style>

 </head>

 <body>

 <img class="image" src="http://img.mukewang.com/547c34c9000171a002560191.jpg" height="191">

 <p class="button">

     <input type="button" value="添加margin: auto;" onClick="document.getElementsByTagName('img')[0].style.margin = 'auto';">

 </p>

 </body>

 </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：


css之absolute


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


css之absolute


css之absolute


参考地址：http://www.imooc.com/learn/192
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