1. 弹性盒子（CSS Flexible Box）：任何元素,都可以通过添加`flex`属性转为弹性盒子。
有了弹性盒子, 通常只需要指定元素的:空间分布方式；内容对齐方式；元素排列顺序，就可以轻易的使用几行代码,实现一个专业,完美的布局。
弹性盒子完全摆脱了元素的显示顺序依赖源码的书写顺序的限制、
弹性布局对移动设置非常友好, 也同样适合于PC端布局。
这个弹性盒子, 就是 弹性容器(Flex Container)，弹性容器为分二种:
display: flex； 块级弹性容器
display: inline-flex； 行内块级弹性容器
弹性元素(Flex item)：弹性容器的子元素, 会自动成为弹性元素
弹性元素必须是弹性容器的直接子元素
任何类型的元素,只要转为弹性元素, 都转为块级元素
下面从实例更直观了解：
实例1
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>弹性容器的二种类型</title>
<style>
/*弹性容器通用样式*/
.container {
border: 2px dashed red;
margin: 15px;
background: #cdc;
}
/*弹性元素通用样式*/
.item {
box-sizing: border-box;
border: 1px solid;
padding: 20px;
background: #ede;
}
/*块级弹性容器*/
.flex {
display: flex;
}
/*行内/内联弹性盒子*/
.inline-flex {
display: inline-flex;
}
</style>
</head>
<body>
<h3>1. 块级_弹性容器</h3>
<div class="container flex">
<span class="item">item1</span>
<span class="item">item2</span>
<span class="item">item3</span>
</div>
<h3>2. 行内块级_弹性容器</h3>
<div class="container inline-flex">
<span class="item">item1</span>
<span class="item">item2</span>
<span class="item">item3</span>
</div>
</body>
</html>运行实例 »
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实例运行效果：
手写代码：
实例2：弹性盒子做导航实例
实例 2
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>弹性容器(盒子)做导航</title>
<style>
/*链接样式重置*/
a {
padding: 5px 10px;
margin: 0 5px;
border-radius: 5px 5px 0 0;
text-decoration-line: none;
background-color: lightgreen;
box-shadow: 2px 0 1px #888;
color: black;
}
a:hover,
/*tab切换进也会激活*/
a:focus,
a:active {
background-color: orangered;
color: white;
}
nav {
display: flex;
border-bottom: 1px solid gray;
}
</style>
</head>
<body>
<nav>
<a href="">首页</a>
<a href="">教学视频</a>
<a href="">社区问答</a>
<a href="">软件下载</a>
<a href="">联系我们</a>
</nav>
</body>
</html>运行实例 »
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实例运行效果：
手写代码：
2. 弹性容器的主轴与交叉轴
主轴：弹性元素流动的方向
主轴尺寸：主轴上弹性元素总长度
主轴起点：弹性元素开始流动的那一端
主轴终点：弹性元素流向的目标那一端、
所有弹性元素必须沿着主轴方向排列
： 交叉轴：与主轴垂直的轴, 所以也叫垂直轴或侧轴或副轴
交叉轴尺寸：垂直轴上弹性元素总长度
交叉轴起点：垂直轴上块级元素开始堆叠的那一端
交叉轴终点：垂直轴上与起点相对应的那一端
所有弹性元素必须沿着交叉轴方向添加
：
下面以实例加以理解:
实例3：弹性容器的主轴方向: 弹性元素的主轴上的排列方向
实例3
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>定义弹性容器的主轴方向: 弹性元素的主轴上的排列方向</title>
<!-- <link rel="stylesheet" href="css/style3.css">-->
<style>
/*弹性容器通用样式*/
.container {
border: 2px dashed red;
margin: 15px;
background: #cdc;
}
/*弹性元素通用样式*/
.item {
box-sizing: border-box;
border: 1px solid;
padding: 20px;
background: #ede;
}
/*块级弹性容器*/
.flex {
display: flex;
}
.row {
flex-direction: row;
}
.row-reverse {
flex-direction: row-reverse;
}
.column {
flex-direction: column;
}
.column-reverse {
flex-direction: column-reverse;
}
</style>
</head>
<body>
<h3>1. row: 默认从左向右,水平排列</h3>
<div class="container flex row">
<span class="item">item1</span>
<span class="item">item2</span>
<span class="item">item3</span>
</div>
<h3>2. row: 从右向左,水平排列</h3>
<div class="container flex row-reverse">
<span class="item">item1</span>
<span class="item">item2</span>
<span class="item">item3</span>
</div>
<h3>3. column: 从下向下,垂直排列</h3>
<div class="container flex column">
<span class="item">item1</span>
<span class="item">item2</span>
<span class="item">item3</span>>
</div>
<h3>4. column-reverse: 从下向上,垂直排列</h3>
<div class="container flex column-reverse">
<span class="item">item1</span>
<span class="item">item2</span>
<span class="item">item3</span>
</div>
</body>
</html>运行实例 »
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运行效果：
手写代码：
实例4：弹性容器实现页面布局之图文混排（弹性元素在主轴方向排列演示）
实例4
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>创建网站首页</title> <link rel="stylesheet" href="css/style2.css"> <link rel="stylesheet" href="css/style4.css"> </head> <body> <!--页眉--> <header> <h1>一丝不挂的博客</h1> </header> <!--导航--> <nav> <a href="">首页</a> <a href="">教学视频</a> <a href="">社区问答</a> <a href="">软件下载</a> <a href="">联系我们</a> </nav> <!--主体--> <main> <article> <img src="images/1.jpg" alt=""> <p>JavaScript 是一门弱类型的动态脚本语言，支持多种编程范式，包括面向对象和函数式编程，被广泛用于 Web 开发。 JavaScript 是一门弱类型的动态脚本语言，支持多种编程范式，包括面向对象和函数式编程，被广泛用于 Web 开发。 JavaScript 是一门弱类型的动态脚本语言，支持多种编程范式，包括面向对象和函数式编程，被广泛用于 Web 开发。 JavaScript 是一门弱类型的动态脚本语言，支持多种编程范式，包括面向对象和函数式编程，被广泛用于 Web 开发。 JavaScript 是一门弱类型的动态脚本语言，支持多种编程范式，包括面向对象和函数式编程，被广泛用于 Web 开发。 </p> <button>立即学习</button> </article> <article> <img src="images/2.jpg" alt=""> <p>Vue是一套用于构建用户界面的渐进式框架, 被设计为可以自底向上逐层应用。</p> <button>立即学习</button> </article> <article> <img src="images/3.jpg" alt=""> <p>Laravel是一套简洁,优雅的PHP Web开发框架, 它可以帮你构建一个完美的网络APP</p> <button>立即学习</button> </article> </main> <!--页脚--> <footer> <!-- ©: 是html实体字符,代表版权符号--> <p>Copyright © 2018 -2021 php中文网</p> </footer> </body> </html>
/*链接样式重置*/
a {
padding: 5px 10px;
margin: 0 5px;
border-radius: 5px 5px 0 0;
text-decoration-line: none;
background-color: lightgreen;
box-shadow: 2px 0 1px #888;
color: black;
}
a:hover,
/*tab切换进也会激活*/
a:focus,
a:active {
background-color: orangered;
color: white;
}
nav {
display: flex;
border-bottom: 1px solid gray;
}
* {
/*参考轮廓线: 不占据页面空间*/
/*outline: 1px solid #ccc;*/
margin: 10px;
padding: 10px;
}
/*将页面中主要布局元素全部转为弹性容器*/
body, nav, main, article {
display: flex;
}
/*设置全局, 内容区主轴垂直, 元素沿主轴排列*/
body, article {
flex-direction: column;
}
/*页脚添加上边框*/
footer {
border-top: 1px solid #ccc;
}
/*导航删除下内边距*/
nav {
padding-bottom: 0;
}运行实例 »
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运行效果：
手写代码：
实例5：弹性容器中弹性元素溢出与创建多行容器
实例5
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>弹性元素溢出与创建多行容器</title> <link rel="stylesheet" href="css/style5.css"> </head> <body> <h1>以主轴水平方向为例演示:</h1> <!--默认: 弹性元素不会在主轴上换行,不会自动调整大小, 当主轴空间不足时, 会从边界溢出--> <h3>1. nowrap: 默认不换行,元素自动缩小适应容器</h3> <div class="container flex row nowrap"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> <span class="item">item7</span> <span class="item">item8</span> <span class="item">item9</span> <span class="item">item10</span> <span class="item">item11</span> </div> <h3>2. wrap: 换行,元素超出容器边界后换到下一行继续显示</h3> <div class="container flex row wrap"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> <span class="item">item7</span> <span class="item">item8</span> <span class="item">item9</span> <span class="item">item10</span> <span class="item">item11</span> </div> <h3>3. wrap-reverse: 换行后,弹性元素在垂直方向反向排列</h3> <div class="container flex row wrap-reverse"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> <span class="item">item7</span> <span class="item">item8</span> <span class="item">item9</span> <span class="item">item10</span> <span class="item">item11</span> </div> <h3>4.row-reverse主轴从右往左，wrap换行</h3> <div class="container flex row-reverse wrap"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> <span class="item">item7</span> <span class="item">item8</span> <span class="item">item9</span> <span class="item">item10</span> <span class="item">item11</span> </div> <h3>5.row-reverse主轴从右往左,wrap-reverse元素在垂直方向反向排列</h3> <div class="container flex row-reverse wrap-reverse"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> <span class="item">item7</span> <span class="item">item8</span> <span class="item">item9</span> <span class="item">item10</span> <span class="item">item11</span> </div> </body> </html>
/*弹性容器通用样式*/
.container {
border: 2px dashed red;
margin: 15px;
background: #cdc;
}
/*弹性元素通用样式*/
.item {
box-sizing: border-box;
border: 1px solid;
padding: 20px;
background: #ede;
}
/*块级弹性容器*/
.flex {
display: flex;
}
.container {
width: 500px;
}
/*不换行*/
.nowrap {
flex-direction: row;
flex-wrap: nowrap;
}
/*换行*/
.wrap {
flex-direction: row;
flex-wrap: wrap;
}
.wrap-reverse {
flex-direction: row;
flex-wrap: wrap-reverse;
}
div:nth-last-of-type(2){
flex-direction: row-reverse;
flex-wrap: wrap;
}
div:last-of-type{
flex-direction: row-reverse;
flex-wrap: wrap-reverse;
}运行实例 »
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运行效果：
手写代码：
注意：弹性元素流体布局的简写：弹性容器的flex-flow属性
格式：flex-flow: 主轴方向 换行方式；如：flex-flow:row nowrap;
即：
实例6：弹性元素在主轴上如何分布
实例6
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>弹性元素在主轴上如何分布</title> <link rel="stylesheet" href="css/style7.css"> </head> <body> <h1>弹性元素在主轴上如何分布:</h1> <h3>1. flex-start: 主轴起点开始水平排列</h3> <p>单行</p> <div class="container flex flex-start"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行</p> <div class="container flex flex-start wrap"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> <hr style="height: 3px; background:green;"> <h3>2. flex-end: 主轴终点开始水平排列</h3> <p>单行</p> <div class="container flex flex-end"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行</p> <div class="container flex flex-end wrap"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> <hr style="height: 3px; background:green;"> <h3>3. center: 将所有弹性元素视为整体,居中显示</h3> <p>单行</p> <div class="container flex center"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行</p> <div class="container flex center wrap"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> <hr style="height: 3px; background:green;"> <h3>4. space-between: 首尾元素紧贴起止点,其它元素平分剩余空间</h3> <p>单行</p> <div class="container flex space-between"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行</p> <div class="container flex space-between wrap"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> <hr style="height: 3px; background:green;"> <h3>5. space-around: 每个元素两边空间相等,相邻元素空间累加</h3> <p>单行</p> <div class="container flex space-around"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行</p> <div class="container flex space-around wrap"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> <hr style="height: 3px; background:green;"> <h3>6. space-evenly: 每个元素, 以及元素到与起止点的空间全部相等</h3> <p>单行</p> <div class="container flex space-evenly"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行</p> <div class="container flex space-evenly wrap"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> </body> </html>
/*弹性容器通用样式*/
.container {
border: 2px dashed red;
margin: 15px;
background: #cdc;
}
/*弹性元素通用样式*/
.item {
box-sizing: border-box;
border: 1px solid;
padding: 20px;
background: #ede;
}
/*块级弹性容器*/
.flex {
display: flex;
}
.container {
width: 550px;
}
/*允许换行*/
.wrap {
flex-wrap: wrap;
}
/*默认值:弹性元素紧贴主轴起点开始排列*/
.flex-start {
justify-content: flex-start;
}
.flex-end {
justify-content: flex-end;
}
.center {
justify-content: center;
}
.space-between {
justify-content: space-between;
}
/*会千万首尾元素与容器边界的空间,只有其它元素之间空间的一半*/
.space-around {
justify-content: space-around;
}
.space-evenly {
justify-content: space-evenly;
}运行实例 »
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运行效果：
手写代码：
实例7：使用弹性元素主轴对齐来改写导航
实例7
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>使用弹性元素主轴对齐来改写导航</title>
<!-- <link rel="stylesheet" href="css/style8.css">-->
<style>
/*链接样式重置*/
a {
padding: 5px 10px;
margin: 0 5px;
border-radius: 5px 5px 0 0;
text-decoration-line: none;
background-color: lightgreen;
box-shadow: 2px 0 1px #888;
color: black;
}
a:hover,
/*tab切换进也会激活*/
a:focus,
a:active {
background-color: orangered;
color: white;
}
nav {
display: flex;
border-bottom: 1px solid gray;
}
/*将导航放在主轴的任意位置上*/
nav {
justify-content: flex-start;
}
nav {
justify-content: flex-end;
}
nav {
justify-content: center;
}
</style>
</head>
<body>
<nav>
<a href="">首页</a>
<a href="">教学视频</a>
<a href="">社区问答</a>
<a href="">软件下载</a>
<a href="">联系我们</a>
</nav>
</body>
</html>运行实例 »
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运行效果：
手写代码：
实例8：弹性元素在垂直方向(交叉轴)上的对齐方式
实例8
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>弹性元素在垂直方向(交叉轴)上的对齐方式</title> <link rel="stylesheet" href="css/style9.css"> </head> <body> <h1>弹性元素在垂直轴上分布方式:</h1> <h3>1. stretch: 默认值, 元素高度自动拉伸充满整个容器</h3> <p>单行容器:</p> <div class="container flex stretch"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行容器:</p> <div class="container flex wrap wrap-stretch"> <!-- 如果你发现元素垂直并未对齐,是因为数字宽度造成, 将1改为2试试--> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> <hr style="height: 3px; background:green;"> <h3>2. flex-start: 元素紧贴容器起点</h3> <p>单行容器:</p> <div class="container flex flex-start"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行容器:</p> <div class="container flex wrap wrap-flex-start"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> <hr style="height: 3px; background:green;"> <h3>3. flex-end: 元素紧贴容器终点</h3> <p>单行容器:</p> <div class="container flex flex-end"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行容器:</p> <div class="container flex wrap wrap-flex-end"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> <hr style="height: 3px; background:green;"> <h3>4. center: 元素中点与垂直轴中点对齐, 居中显示</h3> <p>单行容器:</p> <div class="container flex center"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> </div> <p>多行容器:</p> <div class="container flex wrap wrap-center"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> </div> <hr style="height: 3px; background:green;"> <h3>5. 垂直方向首尾行紧贴起止点,其它行平分剩余空间</h3> <div class="container flex wrap wrap-space-between"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> <span class="item">item7</span> <span class="item">item8</span> <span class="item">item9</span> <span class="item">item10</span> </div> <hr style="height: 3px; background:green;"> <h3>6. 每个元素两边空间相等,相邻元素空间累加</h3> <div class="container flex wrap wrap-space-around"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> <span class="item">item7</span> <span class="item">item8</span> <span class="item">item9</span> <span class="item">item10</span> </div> <hr style="height: 3px; background:green;"> <h3>7. 每个元素, 以及元素到与起止点的空间全部相等</h3> <div class="container flex wrap wrap-space-evenly"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> <span class="item">item7</span> <span class="item">item8</span> <span class="item">item9</span> <span class="item">item10</span> </div> <hr style="height: 3px; background:green;"> <h3>8. 小案例: 结合主轴, 实现空间全部平均分配</h3> <div class="container flex wrap wrap-space-evenly all-align"> <span class="item">item1</span> <span class="item">item2</span> <span class="item">item3</span> <span class="item">item4</span> <span class="item">item5</span> <span class="item">item6</span> <span class="item">item7</span> <span class="item">item8</span> <span class="item">item9</span> <span class="item">item10</span> </div> </body> </html>
@import "public.css";
.container {
width: 550px;
height: 300px;
}
/*允许换行*/
.wrap {
flex-wrap: wrap;
}
/************ 单行容器 ************/
/*1. 单行自动拉伸*/
.stretch {
align-items: stretch;
}
/*2. 单行起点对齐*/
.flex-start {
align-items: flex-start;
}
/*3. 单行终点对齐*/
.flex-end {
align-items: flex-end;
}
/*4. 单行居中对齐*/
.center {
align-items: center;
}
/************ 多行容器 ************/
/*1. 多行自动拉伸*/
.wrap-stretch {
/*每一行的对齐方式*/
align-content: stretch;
}
/*2. 多行起点对齐*/
.wrap-flex-start {
align-content: flex-start;
}
/*3. 多行终点对齐*/
.wrap-flex-end {
align-content: flex-end;
}
/* 4. 多行居中对齐 */
.wrap-center {
align-content: center;
}
/*5. space-between*/
.wrap-space-between {
align-content: space-between;
}
/*6. space-around*/
.wrap-space-around {
align-content: space-around;
}
/*7. space-evenly*/
.wrap-space-evenly {
align-content: space-evenly;
}
/*实战: 元素的水平垂直全部平均对齐*/
.all-align {
justify-content: space-evenly;
align-content: space-evenly;
}运行实例 »
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