css 中position定位_html/css_WEB-ITnose
css html
请看第一个代码<html><head><style type="text/css">h2.pos_left{position:relative;left:-20px}h2.pos_right{position:relative;left:20px}</style></head><body><h2 id="这是位于正常位置的标题">这是位于正常位置的标题</h2><h2 id="这个标题相对于其正常位置向左移动">这个标题相对于其正常位置向左移动</h2><h2 id="这个标题相对于其正常位置向右移动">这个标题相对于其正常位置向右移动</h2><p>相对定位会按照元素的原始位置对该元素进行移动。</p><p>样式 "left:-20px" 从元素的原始左侧位置减去 20 像素。</p><p>样式 "left:20px" 向元素的原始左侧位置增加 20 像素。</p></body></html>如果把上面的代码改为
<html><head><style type="text/css">h2.pos_left{position:fixed;left:-20px}h2.pos_right{position:relative;left:20px}</style></head><body><h2 id="这是位于正常位置的标题">这是位于正常位置的标题</h2><h2 id="这个标题相对于其正常位置向左移动">这个标题相对于其正常位置向左移动</h2><h2 id="这个标题相对于其正常位置向右移动">这个标题相对于其正常位置向右移动</h2><p>相对定位会按照元素的原始位置对该元素进行移动。</p><p>样式 "left:-20px" 从元素的原始左侧位置减去 20 像素。</p><p>样式 "left:20px" 向元素的原始左侧位置增加 20 像素。</p></body></html>以上都是在chrome浏览器的调试图
高手解释为什么出现这种情况，谢谢了。
回复讨论(解决方案)
h2.pos_left{position:fixed;left:-20px}这个是固定定位 ，属于绝对定位的一种，被固定定位的元素已经脱离了原来的文档流。固定定位 是相对于视窗窗口 定位的，所以 不管浏览器如何滚动，他都在相同位置
fixed 的包含块是视窗，不属于文档的流。
XML/HTML code?12345h2.pos_left{position:fixed;left:-20px}
这个是固定定位 ，属于绝对定位的一种，被固定定位的元素已经脱离了原来的文档流。固定定位 是相对于视窗窗口 定位的，所以 不管浏览器如何滚动，他都在相同位置
那为什么在正常位置下的两句话位置反过来了
fixed 的包含块是视窗，不属于文档的流。
在“这是位于正常位置的标题”下面两句话的位置倒过来了。
引用 2 楼 eazyc 的回复:fixed 的包含块是视窗，不属于文档的流。
在“这是位于正常位置的标题”下面两句话的位置倒过来了。
你 把浏览器 窗口 调小 ，出现滚动条 ，就会体会到 固定定位 是什么意思了
引用 4 楼 liulinisgood 的回复:引用 2 楼 eazyc 的回复:fixed 的包含块是视窗，不属于文档的流。
在“这是位于正常位置的标题”下面两句话的位置倒过来了。
你 把浏览器 窗口 调小 ，出现滚动条 ，就会体会到 固定定位 是什么意思了
嗯，试了一下，的确fixed是不会改变位置的，relative会随滚动条上下而动。
在浏览器最大化时候在两幅图中的两句话位置颠倒是不是因为relative需要和标准的相对位置固定，所以就在css 中fixed的段落之上了，理解是否有误（就是第二幅中的黑体三句话的顺序）
position: fixed;
这个是固定在可视区域，这个时候不占据文档流空间，就是“”设置固定定位后会把空间让出来，这个时候，下个H2元素就会占据pos_left的文档空间，就出现了你看到的现象
楼主看下
http://www.w3school.com.cn/css/pr_class_position.asp
生成绝对定位的元素，相对于浏览器窗口进行定位。
另外建议楼主 写css加上 nbsp;HTML>
ie低版本不支持fixed，需要另作处理
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