七、盒模型
在css中盒模型被分为两种，第一种是w3c的标准盒模型，另一种是IE6混杂模式的传统模型。他们都是对元素计算尺寸的模型。但他们的不同是计算的方式不同。
①W3C标准盒模型
clientWidth= width + padding + border;
②IE6混杂模式盒模型
clientWidth= width - padding - border
2、box-sizing：可以选择盒模型
①标准（W3C标准）模式盒模型：box-sizing : border-box（优势：向内扩展，加上border、padding不会影响布局）
②IE6混杂模式盒模型：box-sizing ：content-box
八、弹性盒子flex
实例：
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????margin: 100px; ???????????display: flex; ???????????width: 500px; ???????????height: 500px; ???????????border: 1px solid black; ???????} ????????.item { ???????????flex: 1; ???????????width: 100px; ???????????height: 30px; ???????????border: 1px solid red; ???????????line-height: 30px; ???????????text-align: center; ???????????box-sizing: border-box; ???????????font-size: 30px; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ???????<div class="item">3</div> ???????<div class="item">4</div> ???????<div class="item">5</div> ???</div></body> </html>1、父级(容器)
display:flex;
2、父级身上属性
①flex-direction 决定主轴的方向
flex-direction：row | row-reverse | column | column-reverse
row（默认值）：主轴为水平方向，起点在左端。
row-reverse：主轴为水平方向，起点在右端。
column：主轴为垂直方向，起点在上沿。
column-reverse：主轴为垂直方向，起点在下沿。
实例：
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 100px; ???????????width: 500px; ???????????height: 500px; ???????????border: 1px solid black; ???????????flex-direction: column; ???????} ????????.item { ???????????flex: 1; ???????????width: 100px; ???????????height: 30px; ???????????border: 1px solid red; ???????????line-height: 30px; ???????????text-align: center; ???????????box-sizing: border-box; ???????????font-size: 30px; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ???????<div class="item">3</div> ???????<div class="item">4</div> ???????<div class="item">5</div> ???</div></body> </html>②flex-wrap 是否换行
flex-wrap：nowrap（默认） | wrap | wrap-reverse
默认情况下，项目都排在一条线（又称"轴线"）上。flex-wrap属性定义，如果一条轴线排不下，如何换行。
nowrap（默认）：不换行。
wrap：换行，第一行在上方。
wrap-reverse：换行，第一行在下方。
当设置flex-grow属性的时候wrap失效，flex-basis尽可能按basis值往大了去从而达到折行的目的， flex-shrink会失效 (根据子元素实际的宽度判断是否折行)
实例：
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 100px; ???????????width: 500px; ???????????height: 500px; ???????????border: 1px solid black; ???????????justify-content: center; ???????????align-items: center; ???????????flex-wrap: wrap; ???????} ????????.item { ???????????/* flex: 1; */ ???????????width: 150px; ???????????height: 40px; ???????????border: 1px solid red; ???????????line-height: 40px; ???????????text-align: center; ???????????box-sizing: border-box; ???????????font-size: 30px; ???????????flex-wrap: wrap; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ???????<div class="item">3</div> ???????<div class="item">4</div> ???</div></body> </html>③flex-flow：flex-direction和flex-wrap的简写
默认值：默认值为row nowrap
flex-flow:column wrap;
④justify-content项目在主轴上的对齐方式
justify-content: flex-start | flex-end | center | space-between | space-around;
flex-start（默认值）：左对齐
flex-end：右对齐
center： 居中
space-between：两端对齐，项目之间的间隔都相等。
space-around：每个项目两侧的间隔相等。所以，项目之间的间隔比项目与边框的间隔大一倍。（手拉手）
实例：
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 100px; ???????????width: 500px; ???????????height: 500px; ???????????border: 1px solid black; ???????????justify-content: center; ???????} ????????.item { ???????????/* flex: 1; */ ???????????width: 150px; ???????????height: 40px; ???????????border: 1px solid red; ???????????line-height: 40px; ???????????text-align: center; ???????????box-sizing: border-box; ???????????font-size: 30px; ???????????flex-wrap: wrap; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ???</div></body> </html>⑤align-items 在侧轴上如何对齐
align-items: flex-start | flex-end | center | baseline | stretch;
flex-start：交叉轴的起点对齐。
flex-end：交叉轴的终点对齐。
center：交叉轴的中点对齐。
baseline: 项目的第一行文字的基线对齐。
stretch（默认值）：如果项目未设置高度或设为auto，将占满整个容器的高度。
实例：
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 100px; ???????????width: 500px; ???????????height: 500px; ???????????border: 1px solid black; ???????????justify-content: center; ???????????align-items: center; ???????} ????????.item { ???????????/* flex: 1; */ ???????????width: 150px; ???????????height: 40px; ???????????border: 1px solid red; ???????????line-height: 40px; ???????????text-align: center; ???????????box-sizing: border-box; ???????????font-size: 30px; ???????????flex-wrap: wrap; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ???</div></body> </html>⑥align-content 多根轴线的对齐方式
align-content: flex-start | flex-end | center | space-between | space-around | stretch;
flex-start：与交叉轴的起点对齐。
flex-end：与交叉轴的终点对齐。
center：与交叉轴的中点对齐。
space-between：与交叉轴两端对齐，轴线之间的间隔平均分布。
space-around：每根轴线两侧的间隔都相等。所以，轴线之间的间隔比轴线与边框的间隔大一倍。
stretch（默认值）：轴线占满整个交叉轴。
align-content属性定义了多根轴线的对齐方式。如果项目只有一根轴线，该属性不起作用。
实例：
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 100px; ???????????width: 500px; ???????????height: 500px; ???????????border: 1px solid black; ???????????justify-content: center; ???????????flex-wrap: wrap; ???????????align-content: center; ???????} ????????.item { ???????????/* flex: 1; */ ???????????width: 150px; ???????????height: 40px; ???????????border: 1px solid red; ???????????line-height: 40px; ???????????text-align: center; ???????????box-sizing: border-box; ???????????font-size: 30px; ???????????flex-wrap: wrap; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ???????<div class="item">3</div> ???????<div class="item">4</div> ???????<div class="item">5</div> ???</div></body> </html>实例：用flex实现元素水平垂直居中
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 50px auto; ???????????width: 500px; ???????????height: 500px; ???????????border: 1px solid black; ???????????justify-content: center; ???????????align-items: center; ???????} ????????.item { ???????????/* flex: 1; */ ???????????width: 200px; ???????????height: 200px; ???????????border: 1px solid red; ???????????box-sizing: border-box; ???????????flex-wrap: wrap; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item"></div> ???</div></body> </html>3、子级(项目)身上的属性
①flex-grow：放大比例
根据所设置的比例分配盒子所剩余的空间
flex-grow: number
实例：两栏布局
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 50px auto; ???????????width: 500px; ???????????height: 300px; ???????????border: 1px solid black; ???????} ???????.item { ???????????/* flex: 1; */ ???????????height: 30px; ???????????box-sizing: border-box; ???????????flex-wrap: wrap; ???????} ???????.item:nth-of-type(1){ ???????????width: 200px; ???????????border: 1px solid red; ???????} ???????.item:nth-of-type(2){ ???????????flex-grow: 1; ???????????border: 1px solid green; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ??????????</div></body> </html>实例：
flex-direction: row-reverse;
实例：
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 50px auto; ???????????width: 500px; ???????????height: 300px; ???????????border: 1px solid black; ???????????flex-direction: column; ???????} ???????.item { ???????????/* flex: 1; */ ???????????box-sizing: border-box; ???????} ???????.item:nth-of-type(1){ ???????????height: 100px; ???????????border: 1px solid red; ???????} ???????.item:nth-of-type(2){ ???????????flex-grow: 1; ???????????border: 1px solid green; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ??????????</div></body> </html>实例：
flex-direction: column-reverse;
实例：三栏布局
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 50px auto; ???????????width: 500px; ???????????height: 300px; ???????????border: 1px solid black; ???????} ???????.item { ???????????/* flex: 1; */ ???????????height: 30px; ???????????box-sizing: border-box; ???????????flex-wrap: wrap; ???????} ???????.item:nth-of-type(1){ ???????????width: 100px; ???????????border: 1px solid red; ???????} ???????.item:nth-of-type(2){ ???????????flex-grow: 1; ???????????border: 1px solid green; ???????} ???????.item:nth-of-type(3){ ???????????flex-grow: 2; ???????????border: 1px solid green; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ???????<div class="item">3</div> ??????????</div></body> </html>②flex-shrink：缩小比例
多出盒子的部分，按照比例的大小砍掉相应的大小，即比例越大，被砍的越大，默认值1；
缩减的宽度=(flex-shrink1 * width1) /( flex-shrink1 * width1 + flex-shrink2 * width2) * moreWidth
实例：
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 50px auto; ???????????width: 500px; ???????????height: 300px; ???????????border: 1px solid black; ???????} ???????.item { ???????????flex-grow: 1; ???????????width: 200px; ???????????box-sizing: border-box; ???????????height: 30px; ???????} ???????.item:nth-of-type(1){ ???????????flex-shrink: 1; ???????????border: 1px solid red; ???????} ???????.item:nth-of-type(2){ ???????????flex-shrink: 4; ???????????border: 1px solid green; ???????} ???????.item:nth-of-type(3){ ???????????flex-shrink: 1; ???????????border: 1px solid blue; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ??????????<div class="item">3</div> ????????</div></body> </html>③flex-basis：伸缩基准值
伸缩基准值.项目占据主轴的空间
该属性设置元素的宽度或高度，当然width也可以用来设置元素宽度，如果元素上同时出现了width 和flex-basis那么flex-basis会覆盖width的值
子元素宽度尽可能按照basis来如果基准值相加大于容器宽度那么 下面由下面公式分配宽度给子元素 ( flex-basis/(flex-basis相加) ) * 容器的宽度
实例：
<!DOCTYPE html><html lang="en"> <head> ???<meta charset="UTF-8"> ???<meta name="viewport" content="width=device-width, initial-scale=1.0"> ???<meta http-equiv="X-UA-Compatible" content="ie=edge"> ???<title>Document</title> ???<style> ???????* { ???????????padding: 0; ???????????margin: 0; ???????} ????????.wrapper { ???????????display: flex; ???????????margin: 50px auto; ???????????width: 500px; ???????????height: 300px; ???????????border: 1px solid black; ???????} ???????.item { ???????????/* flex: 1; */ ???????????height: 30px; ???????????box-sizing: border-box; ???????} ???????.item:nth-of-type(1){ ???????????flex-basis: 50%; ???????????border: 1px solid red; ???????} ???????.item:nth-of-type(2){ ???????????flex-basis: 20%; ???????????border: 1px solid green; ???????} ???????.item:nth-of-type(3){ ???????????flex-basis: 30%; ???????????border: 1px solid green; ???????} ???</style></head> <body> ???<div class="wrapper"> ???????<div class="item">1</div> ???????<div class="item">2</div> ???????<div class="item">3</div> ??????????</div></body> </html>④flex：是flex-grow, flex-shrink 和 flex-basis的简写
flex:1 —> flex:1 1 0%;
flex:3 —> flex:3 1 0%;
注意:flexbox布局和原来的布局是两个概念，部分css属性在flexbox盒子里面不起作用，eg：float， clear， column,vertical-align 等等
⑤order：排列顺序
number定义项目的排列顺序。数值越小，排列越靠前，默认为0
order: number;
⑥align-self ：单个项目对齐方式
align-self: auto | flex-start | flex-end | center | baseline | stretch;
align-self属性允许单个项目有与其他项目不一样的对齐方式，可覆盖align-items属性。默认值为auto，表示继承父元素的align-items属性，如果没有父元素，则等同于stretch。
神奇的Css3（4） 弹性布局
原文地址：https://www.cnblogs.com/wangzhenling/p/8989777.html