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HomeWeb Front-endHTML TutorialCss3之基础-8 Css 浮动(定位,浮动定位)_html/css_WEB-ITnose

一、CSS 定位概述


定位概述

  - 定位: 定义元素框相对于其正常位置应该出现的位置,或者相对于父元素、另一个元素甚至浏览器窗口本身的位置

  - 普通流定位

  - 浮动定位

  - 相对定位

  - 绝对定位


普通流定位

  - 页面中的块级元素框从上到下一个接一个地排列

      - 每一个块级元素都会出现在一个新行中(比如

元素、

元素)

      - 元素框之间的垂直距离是由框的垂直外边距计算出来的

  - 内联元素将在一行中从左到右排列水平布置

      - 不需要从新行开始

      - 可以使用水平内边距、边框和外边距调整它们的间距


二、CSS 浮动定位


浮动概述

  - 浮动定位是指

      - 将元素排除在普通流之外,即元素将脱离标准文档流

      - 元素将不在页面占用空间

      - 将浮动元素放置在包含框的左边或者右边

      - 浮动元素依旧位于包含框之内

  - 浮动的框可以向左或向右移动,直到它的外边缘碰到包含框或另一个浮动框的边框为止

      - 经常使用它来实现特殊的定位效果


浮动定位

  - 包含框中有三个元素框,如果把框1向右浮动,则它脱离文档流并且向右移动,直到它的右边缘

  - 当框1向左浮动时,它脱离文档流并且向左移动,直到它的左边缘碰到包含框的左边缘

  - 因为框1不再处于文档流中,所以它不占据空间,实际上覆盖住了框2,使框2从视图中消失

  - 如果把所有三个框都向左移动,那么框1向左浮动直到碰到包含框,另外两个框向左浮动直到碰到前一个浮动框: 三个框在同一行上显示

  - 如果包含框太窄,那么其它浮动块会自动向下移动,直到有足够的空间(左图)

  - 如果浮动元素的高度不同,那么当它们向下移动时可能被其他浮动元素"卡住"(右图)

  - 浮动元素的外边缘不会超过其父元素的内边缘

  - 浮动元素不会互相重叠

  - 浮动元素不会上下浮动


float属性

  - 如果需要设置框浮动在包含框的左边或者右边,可以通过float属性来实现

  - float 属性定义元素在哪个方向浮动

      - 在 CSS 中,任何元素都可以浮动

  - float: none/left/right;


clear属性

  - clear 属性用于清除浮动所带来的影响

  - clear: none/left/right/both;

      - 定义了元素的哪边上不允许出现浮动元素


float 与 overflow

  - 包含框内的元素被应用了float之后,包含框的高度会发生变化

  - 设置包含框内的overflow属性


总结:本章内容主要介绍了 Css (定位,浮动定位)。

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