HTML页面布局基础_html/css_WEB-ITnose
本篇博文主要整理一下html页面布局的基础知识。虽然这些知识基本都懂，但是实际用起来，其中的一些细节老是注意不到(>_
盒子模型
盒子模型是css中一个重要的概念，理解了盒子模型才能更好的排版。盒子模型范围包括： border、padding、margin、content 。盒子模型有两种，分别是IE（怪异模式）盒子模型和标准盒子模型。两者的区别是，IE盒子模型content部分包含 padding 和 border ，而标准盒子模型不包括！css3的 border-sizing 属性可以选择特定盒模型： content-boxing （默认 标准盒子模型）； border-boxing （IE盒子模型）
<!DOCTYPE html><htmllang="en"><head><metacharset="UTF-8"><title>box</title></head><style>/* 标准模式 */.content-box{ box-sizing: content-box; width:200px; height:100px; margin:20px; padding:30px; border:10px solid green; }/* 怪异模式 */.border-box{ box-sizing: border-box; -moz-box-sizing:border-box; /* Firefox */-webkit-box-sizing:border-box; /* Safari */width:200px; height:100px; margin:20px; padding:30px; border:10px solid green; }</style><body><divclass="content-box">标准模式</div><divclass="border-box">怪异模式</div></body></html>呈现效果
标准模式
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content width: 200
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content height: 100
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左border到右border长度为： (10+30)*2 + 200
怪异模式
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content width: 120
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content height: 20
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左border到右border长度为： (10+30)*2 + 120
POSITION
这个属性定义建立元素布局所用的定位机制。任何元素都可以定位，不过 绝对（absolute）或固定（fixed） 元素会生成 一个块级框 ，而不论该元素本身是什么类型。相对定位元素会相对于它在正常流中的默认位置偏移。
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static：默认值。没有定位，元素出现在正常的流中（忽略 top, bottom, left, right 或者 z-index 声明）
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absolute：生成绝对定位的元素， 相对于static定位以外 的第一个父元素进行定位
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relative：生成相对定位的元素，相对于其 本身位置 进行定位
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fixed：生成绝对定位的元素，相对于 浏览器窗口 进行定位
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inherit：规定应该从父元素继承 position 属性的值
相对定位
相对定位比较简单，对应position属性的relative值，如果对一个元素进行相对定位，它将出现在他所在的位置上，然后可以通过设置垂直或水平位置，让这个元素相对于它自己移动， 在使用相对定位时，无论元素是否移动，元素在文档流中占据原来空间，只是表现会改变 。
<!-- 普通流 --><divstyle="border: solid 1px #0e0; width:200px;"><divstyle="height: 100px; width: 100px; background-color: Red;"></div><divstyle="height: 100px; width: 100px; background-color: Green;"></div><divstyle="height: 100px; width: 100px; background-color: Red;"></div></div>
<!-- 相对定位 --><divstyle="border: solid 1px #0e0; width:200px;"><divstyle="height: 100px; width: 100px; background-color: Red;"></div><divstyle="height: 100px; width: 100px; background-color: Green; position:relative; top:20px; left:20px;"></div><divstyle="height: 100px; width: 100px; background-color: Red;"></div></div>
绝对定位
相对定位可以看作特殊的普通流定位，元素位置是相对于他在普通流中位置发生变化，而 绝对定位使元素的位置与文档流无关，也不占据文档流空间，普通流中的元素布局就像绝对定位元素不存在一样。
绝对定位的元素的位置是相对于距离他最近的非static祖先元素位置决定的。也就是说离其最近的祖先元素只要position属性不是static，都可以作为绝对定位的参照标准！如果元素没有已定位的祖先元素，那么他的位置就相对于初始包含块儿（body或html）元素。
因为绝对定位与文档流无关，所以绝对定位的元素可以覆盖页面上的其他元素，可以通过z-index属性控制叠放顺序，z-index越高，元素位置越靠上。
<!-- 绝对定位 --><divstyle="border: solid 1px #0e0; width:200px; position:relative;"><divstyle="height: 100px; width: 100px; background-color: Red;"></div><divstyle="height: 100px; width: 100px; background-color: Green; position:absolute; top:20px; left:20px;"></div><divstyle="height: 100px; width: 100px; background-color: Yellow;"></div></div>
固定定位
固定定位对应position属性的fixed值，固定定位其实是一种特殊的绝对定位，固定定位的元素也不包含在普通文档流中，包含块儿是视口（viewport）
注意：该属性不兼容IE6
参考
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学习CSS布局
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css3 box-sizing属性
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CSS布局 ——从display，position， float属性谈起
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