1. 背景颜色  
 1.1 背景颜色样式  
在Bootstrap  5 中 ,  可以使用以下类来设置背景颜色 : 
*  1.  . bg-primary :    设置为主要的背景颜色 ( # 007 bff ,  深蓝色 ) . 
*  2.  . bg-secondary :  设置为次要的背景颜色 ( # 6 c757d ,  灰色 ) . 
*  3.  . bg-success :    设置为成功的背景颜色 ( # 28 a745 ,  绿色 ) . 
*  4.  . bg-danger :     设置为危险的背景颜色 ( # dc3545 ,  红色 ) . 
*  5.  . bg-warning :    设置为警告的背景颜色 ( # ffc107 ,  黄色 ) . 
*  6.  . bg-info :       设置为信息的背景颜色 ( # 17 a2b8 ,  青色 ) . 
*  7.  . bg-light :      设置为浅色的背景颜色 ( # f8f9fa ,  浅灰色 ) . 
*  8.  . bg-dark :       设置为白色的背景颜色 ( # 343 a40 ,  深灰色 ) . 
*  9.  . bg-dark :       用于将元素的背景颜色设置为白色 . 
*  10.  . bg-transparent :  用于将元素的背景颜色设置为透明 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  背景颜色</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
    < style> 
        .container div  { 
            margin-bottom :  10px; 
        } 
     </ style>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " bg-primary text-white" >  .bg-primary</ div>  
    < div  class = " bg-secondary text-white" >  .bg-secondary</ div>  
    < div  class = " bg-success text-white" >  .bg-success</ div>  
    < div  class = " bg-danger text-white" >  .bg-danger</ div>  
    < div  class = " bg-warning text-dark" >  .bg-warning</ div>  
    < div  class = " bg-info text-dark" >  .bg-info</ div>  
    < div  class = " bg-light text-dark" >  .bg-light</ div>  
    < div  class = " bg-dark text-white" >  .bg-dark</ div>  
</ div>  
</ body>  
</ html>  
  
 
 1.2 颜色渐变  
在bootstrap  5 中 ,  . bg-gradient类可以设置背景颜色渐变 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  背景颜色渐变</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " p-3 mb-2 bg-primary bg-gradient text-white" >  .bg-primary</ div>  
    < div  class = " p-3 mb-2 bg-secondary bg-gradient text-white" >  .bg-secondary</ div>  
    < div  class = " p-3 mb-2 bg-success bg-gradient text-white" >  .bg-success</ div>  
    < div  class = " p-3 mb-2 bg-danger bg-gradient text-white" >  .bg-danger</ div>  
    < div  class = " p-3 mb-2 bg-warning bg-gradient text-dark" >  .bg-warning</ div>  
    < div  class = " p-3 mb-2 bg-info bg-gradient text-dark" >  .bg-info</ div>  
    < div  class = " p-3 mb-2 bg-light bg-gradient text-dark" >  .bg-light</ div>  
    < div  class = " p-3 mb-2 bg-dark bg-gradient text-white" >  .bg-dark</ div>  
    < div  class = " p-3 mb-2 bg-white bg-gradient text-dark" >  .bg-white</ div>  
</ div>  
</ body>  
</ html>  
  
 
 2. 边框  
 2.1 边框样式  
在Bootstrap  5 中 ,  用于设置边框的相关类名及其作用 : 
*  1.  border :  简单的边框样式 ,  通常与其他类一起使用 ,  如 :  border  border-primary . 
*  2.  border- < color > :  设置特定颜色的边框 ,  如 :  border-primary、border-secondary等 . 
*  3.  border- < side > :  设置特定边的边框 ,  如 :  border-top ,  border-start ,  border-bottom ,  border-end ,  只应用于相应的边 . 
*  4.  border- < side > - 0 :  移除特定边的边框 ,  如 :  border-top- 0 ,  border-right- 0 ,  border-bottom- 0 ,  border-left- 0. 
*  5.  border- < size > :  设置特定尺寸的边框 ,  有几个预定义的尺寸类可用 ,  如 :  border- 1 ,  border- 2 ,  border- 3 等 . 
     border-start :  用于设置元素的开始边的边框样式 .  start对应元素的右边框 . 
     border-end :  用于设置元素的结束边的边框样式 .  end对应元素的左边框 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  边框</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
    < style> 
        span  { 
            display :  inline-block; 
            width :  75px; 
            height :  75px; 
            margin :  6px; 
            background-color :  #f9f9f9; 
        } 
     </ style>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < span  class = " border border-primary" > </ span>  
    < span  class = " border border-primary" > </ span>  
    < span  class = " border border-primary border-top-0" > </ span>  
    < span  class = " border border-primary border-end-0" > </ span>  
    < span  class = " border border-primary border-bottom-0" > </ span>  
    < span  class = " border border-primary border-start-0" > </ span>  
    < br>  
    < span  class = " border-primary border-top " > </ span>  
    < span  class = " border-primary border-end" > </ span>  
    < span  class = " border-primary border-bottom" > </ span>  
    < span  class = " border-primary border-start" > </ span>  
</ div>  
</ body>  
</ html>  
  
 
 2.2 圆角边框  
在  Bootstrap  5 中 ,  设置圆角边框的相关类名及其介绍 : 
*  1.  . rounded :  用于添加一个圆角边框效果 ,  将元素的边角变得更圆滑 . 
      rounded-x :  用于设置圆角的大小 ,  x取值范围 0 - 5. 
*  2.  . rounded-top :  用于添加一个圆角边框效果 ,  只影响元素的顶部边角 ,  使其变得更圆滑 . 
*  3.  . rounded-end :  用于添加一个圆角边框效果 ,  只影响元素的尾部 ( 朝向右侧的边 ) 边角 ,  使其变得更圆滑 . 
*  4.  . rounded-bottom :  用于添加一个圆角边框效果 ,  只影响元素的底部边角 ,  使其变得更圆滑 . 
*  5.  . rounded-start :  用于添加一个圆角边框效果 ,  只影响元素的起始 ( 朝向左侧的边 ) 边角 ,  使其变得更圆滑 . 
*  6.  . rounded-circle :  类用于将元素变为一个圆形 ,  效果就像是将矩形的边角完全变圆 . 
*  7.  . rounded-pill :  用于将元素变为一个类似椭圆形的形状 ,  边角变得更圆滑 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  圆角</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
    < style> 
        div > div  { 
            display :  inline-block; 
            width :  75px; 
            height :  75px; 
            background-color :  #7fbce1; 
            margin :  10px 10px; 
        } 
     </ style>  
</ head>  
< body>  
< div  class = " container" >  
    < div  class = " rounded" > </ div>  
    < div  class = " rounded-top rounded-4" > </ div>  
    < div  class = " rounded-end rounded-4" > </ div>  
    < div  class = " rounded-bottom rounded-4" > </ div>  
    < div  class = " rounded-start rounded-4" > </ div>  
    < div  class = " rounded-circle " > </ div>  
    < div  class = " rounded-pill"   style = " height :  75px;  width :  120px" > </ div>  
</ div>  
</ body>  
</ html>  
  
 
 3. 浮动  
 3.1 浮动样式  
在Bootstrap  5 中 ,  用于设置浮动的相关类名及其作用 : 
*  1.  . float-end :  用于将元素向右浮动 . 
     通过将该类应用于元素 ,  可以让元素靠右侧对齐 ,  并允许其他元素环绕在其左侧 . 
     
*  2.  . float-start :  用于将元素向左浮动 . 
     通过将该类应用于元素 ,  可以让元素靠左侧对齐 ,  并允许其他元素环绕在其右侧 . 
     
*  3.  . float-none :  不设置浮动 ,  元素将按照正常文档流排列 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  浮动</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
    < style> 
        span  { 
            display :  inline-block; 
            height :  100px; 
            width :  100px; 
            background-color :  aqua; 
        } 
     </ style>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " border border-1" >  
        < span  class = " float-start border border-1" > </ span>  
        < span  class = " float-end border border-1" > </ span>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 3.2 清除浮动  
在Bootstrap  5 中 ,  . clearfix类用于清除浮动效果 . 
当父元素包含浮动元素时 ,  可能会出现布局混乱的问题 ,  这时可以在父元素上应用 . clearfix类来清除其子元素的浮动效果 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  清除浮动</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
    < style> 
        span  { 
            display :  inline-block; 
            height :  100px; 
            width :  100px; 
            background-color :  aqua; 
        } 
     </ style>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " clearfix border border-1" >  
        < span  class = " float-start border border-1" > </ span>  
        < span  class = " float-end border border-1" > </ span>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 3.3 响应式浮动  
在Bootstrap  5 中 ,  响应式浮动相关的类名及其介绍 : 
*  1.  . float-sm-end :   在小屏幕    ( > = 576 px ) 时 ,   将元素向右浮动 . 
*  2.  . float-md-end :   在中等屏幕  ( > = 768 px ) 时 ,   将元素向右浮动 . 
*  3.  . float-lg-end :   在大屏幕    ( > = 992 px ) 时 ,   将元素向右浮动 . 
*  4.  . float-xl-end :   在超大屏幕  ( > = 1200 px ) 时 ,  将元素向右浮动 . 
*  5.  . float-xxl-end :  在特大屏幕  ( > = 1400 px ) 时 ,  将元素向右浮动 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  响应式浮动</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
  < div  class = " row" >  
    < div  class = " col-12" >  
      < div  class = " float-sm-end m-2 bg-info" >  小屏幕向右浮动</ div>  
    </ div>  
    < div  class = " col-12" >  
      < div  class = " float-md-end m-2 bg-info" >  中等屏幕向右浮动</ div>  
    </ div>  
    < div  class = " col-12" >  
      < div  class = " float-lg-end m-2 bg-info" >  大屏幕向右浮动</ div>  
    </ div>  
    < div  class = " col-12" >  
      < div  class = " float-xl-end m-2 bg-info" >  超大屏幕向右浮动</ div>  
    </ div>  
  </ div>  
</ div>  
</ body>  
</ html>  
  
 
 4. 宽度  
在Bootstrap  5 中 ,  可以使用 . w- * 类名来设置元素的固定宽度或最大宽度 . 
下面是一些常用的宽度类名的介绍 : 
-  . w- 25 :  将元素的宽度设置为 25 % . 
-  . w- 50 :  将元素的宽度设置为 50 % . 
-  . w- 75 :  将元素的宽度设置为 75 % . 
-  . w- 100 :  将元素的宽度设置为 100 % . 
-  . mw-auto :  将元素的最大宽度设置为自动计算 ,  根据内容来确定宽度 . 
-  . mw- 100 :  将元素的最大宽度设置为 100 % . 
这些类名可以与其他Bootstrap类名一起使用 ,  例如网格系统的类名 . col- * ,  以实现自定义的宽度布局 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  宽度</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " row" >  
        < div  class = " col-12" >  
            < div  class = " m-2 w-25 bg-info" >  宽度为 25%</ div>  
        </ div>  
        < div  class = " col-12" >  
            < div  class = " m-2 w-50 bg-info" >  宽度为 50%</ div>  
        </ div>  
        < div  class = " col-12" >  
            < div  class = " m-2 w-75 bg-info" >  宽度为 75%</ div>  
        </ div>  
        < div  class = " col-12" >  
            < div  class = " m-2 w-100 bg-info" >  宽度为 100%</ div>  
        </ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 5. 高度  
在Bootstrap  5 中 ,  可以使用 . h- * 类名来设置元素的固定高度或最大高度 . 
下面是一些常用的高度类名的介绍 : 
-  . h- 25 :  将元素的高度设置为 25 % . 
-  . h- 50 :  将元素的高度设置为 50 % . 
-  . h- 75 :  将元素的高度设置为 75 % . 
-  . h- 100 :  将元素的高度设置为 100 % . 
-  . mh-auto :  将元素的最大高度设置为自动计算 ,  根据内容来确定高度 . 
-  . mh- 100 :  将元素的最大高度设置为 100 % . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  高度</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " row" >  
        < div  class = " col-12" >  
            < div  class = "  w-25 h-25 bg-info" >  高度为 25%</ div>  
        </ div>  
        < div  class = " col-12" >  
            < div  class = "  w-50 h-50 bg-info" >  高度为 50%</ div>  
        </ div>  
        < div  class = " col-12" >  
            < div  class = "  w-75 h-75 bg-info" >  高度为 75%</ div>  
        </ div>  
        < div  class = " col-12" >  
            < div  class = "  w-100 h-100 bg-info" >  高度为 100%</ div>  
        </ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 6. 间距  
间距设置可以通过以下方式进行 : 
-  { property } { sides } - { size } :  设置小屏幕 ( xs ) 的间距 . 
-  { property } { sides } - { breakpoint } - { size } :  设置特定屏幕宽度 ( sm ,  md ,  lg ,  xl或xxl ) 的间距 . 
  property :  表示属性 ,  可以是m ( margin ,  外间距 ) ,  p ( padding ,  内间距 ) . 
  sides :     表示方向 ,  可以是tb ( 下 ) ,  s ( 左 ) ,  e ( 右 ) ,  x ( 水平 ) ,  y ( 垂直 ) ,  或blank ( 所有方向 ) . 
  size :      表示大小 ,  可以是  0 ,  1 ,  2 ,  3 ,  4 ,  5 或auto . 
            0  -  设置  margin  或  padding  为  0 
            1  -  设置  margin  或  padding  为  $spacer  *  .25 
            2  -  设置  margin  或  padding  为  $spacer  *  .5 
            3  -  设置  margin  或  padding  为  $spacer 
            4  -  设置  margin  或  padding  为  $spacer  *  1.5 
            5  -  设置  margin  或  padding  为  $spacer  *  3 
            $spacer是Bootstrap中预定义的间距变量 ( 默认为 :  1 rem ,  一般为 16 px ) 
            在实际使用中 ,  你可以根据需要自定义这些变量的值 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  间距</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " mx-auto bg-info w-25 text-center" >  用户注册</ div>  
    < form>  
        < div  class = " form-row" >  
            < div  class = " form-group" >  
                
                < p  class = " mt-2" >  
                    < label  for = " text" >  邮箱:</ label>  
                    < input  type = " text"   class = " form-control-sm"   id = " text"   placeholder = " email" >  
                </ p>  
                
                < label  for = " color"   class = " mt-2" >  颜色:</ label>  
                < input  type = " color"   id = " color"   class = " form-control-sm"   style = " width :  60px; padding :  4px; "  
                       autocomplete = " off"  
                       value = " #656565" >  
            </ div>  
        </ div>  
    </ form>  
</ div>  
</ body>  
</ html>  
  
 
 7. Flex布局  
 7.1 弹性布局样式  
弹性盒子由容器和其内部的项目组成 . 
弹性容器内包含了一个或多个弹性子元素 . 
在Bootstrap  5 中 ,  d-flex类用于创建一个弹性盒子容器 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  弹性布局</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    
    < div  class = " d-flex p-3 bg-secondary text-white" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.2 行内弹性容器  
在Bootstrap  5 中 ,  d-inline-flex类用于创建一个行内的弹性容器 ,  该容器内的子元素将以弹性盒模型进行布局 . 
弹性盒模型可以让子元素在容器中自动调整大小 ,  并根据设定的规则进行排列 . 
具体来说 ,  d-inline-flex类将一个元素的display属性设置为 "inline-flex" ,  使其以行内的方式展示 ,  并具有弹性盒的特性 . 
使用d-inline-flex可以方便地创建一些灵活的布局 ,  比如一行排列的图标 ,  按钮 ,  文本等元素 ,  
它们可以自动适应容器的大小 ,  并根据需要进行调整和重新排列 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  行内弹性容器</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " d-inline-flex p-3 bg-secondary text-white" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.3 水平对齐  
在Bootstrap  5 中 ,  设置弹性子元素水平显示的相关类名及其介绍 : 
*  1.  . flex-row :  默认 ,  设置子元素向右对齐 . 
*  2.  . flex-row-reverse :  用于设置子元素向右对齐 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  水平方向对齐</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
  < div  class = " d-flex flex-row bg-secondary mb-3" >  
    < div  class = " p-2 bg-info" >  Flex item 1</ div>  
    < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
    < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
  </ div>  
  < div  class = " d-flex flex-row-reverse bg-secondary" >  
    < div  class = " p-2 bg-info" >  Flex item 1</ div>  
    < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
    < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
  </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.5 垂直对齐  
在Bootstrap  5 中 ,  用户设置弹性子元素垂直显示的相关类名及其介绍 : 
*  1.  . flex-column :  默认 ,  子元素沿着垂直方向从上到下排列显示 . 
*  2.  . flex-column-reverse :  子元素按照倒序的方式从下到上排列显示 . 
*  设置之后 ,  子元素将会占据父容器的整行宽度 ,  并依次垂直排列显示 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  垂直方向对齐</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " d-flex flex-column mb-3" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
    < div  class = " d-flex flex-column-reverse" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.6 内容排列  
在Bootstrap  5 中 ,  . justify-content- * 类用于修改弹性容器内子元素的排列方式 . 
相关类名及其介绍 : 
*  1.  . justify-content-start :  默认 ,  表示子元素在容器的起始位置对齐 . 
*  2.  . justify-content-center :  用于将子元素在容器的中间位置对齐 . 
*  3.  . justify-content-end :    用于将子元素在容器的末尾位置对齐 . 
*  4.  . justify-content-between :  这个类将子元素平均分配在容器内 ,  并在首尾两端留下空白间距 . 
*  5.  . justify-content-around :  这个类将子元素平均分配在容器内 ,  并在它们之间以及首尾两端留下相等的空白间距 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  内容排列</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " d-flex justify-content-start bg-secondary mb-3" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
    < div  class = " d-flex justify-content-end bg-secondary mb-3" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
    < div  class = " d-flex justify-content-center bg-secondary mb-3" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
    < div  class = " d-flex justify-content-between bg-secondary mb-3" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
    < div  class = " d-flex justify-content-around bg-secondary mb-3" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.7 等宽  
在Bootstrap  5 中 ,  . flex-fill类用于强制将弹性子元素的宽度设置为相等的值 ,  使它们在水平方向上占据相同的空间 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  等宽</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " d-flex" >  
        < div  class = " p-2 bg-info flex-fill" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning flex-fill" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary flex-fill" >  Flex item 3</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.8 分配空间  
 7.8.1 扩展  
在Bootstrap  5 中 ,  . flex-grow- * 类用于设置弹性子元素在弹性容器中分配剩余空间的比例 . 
相关类名及其介绍 : 
*  1.  . flex-grow- 0 :  使弹性子元素不具有扩展能力 ,  即不会分配任何剩余空间给该元素 . 
*  2.  . flex-grow- 1 :  使弹性子元素可以根据剩余空间进行等比例扩展 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  扩展</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " d-flex mb-3" >  
        < div  class = " p-2 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        
        < div  class = " p-2 flex-grow-1 bg-primary" >  Flex item 3</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.8.2 收缩  
在Bootstrap  5 中 ,  . flex-grow- * 类用于定义弹性盒子项目在空间不足时的收缩比例 . 
相关类名及其介绍 : 
*  1.  flex-shrink- 1 :  默认 ,  所有项目都具有这个类 ,  表示项目将按比例收缩以适应容器的空间 . 
*  2.  flex-shrink- 0 :  表示该项目不会收缩 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  Title</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
    < style> 
        .p-2  { 
            width :  500px; 
        } 
     </ style>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " d-flex" >  
        < div  class = " flex-shrink-1 bg-info p-2" >  项目 1</ div>  
        < div  class = " flex-shrink-1 bg-warning p-2" >  项目 2</ div>  
        < div  class = " flex-shrink-1 bg-primary p-2" >  项目 3</ div>  
    </ div>  
    < div  class = " d-flex" >  
        < div  class = " flex-shrink-0 bg-info p-2" >  项目 1</ div>  
        < div  class = " flex-shrink-0 bg-warning p-2" >  项目 2</ div>  
        < div  class = " flex-shrink-0 bg-primary p-2" >  项目 3</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.9 排序  
在Bootstrap  5 中 ,  . order- * 类可用于设置弹性子元素的排序 . 
相关类名及其介绍 : 
-  . order- 1 :  将子元素的排序设置为 1 ( 最大的排序权重 ) . 
-  . . . 
-  . order- 12 :  将子元素的排序设置为 12 ( 最小的排序权重 ) . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  排序</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " d-flex mb-3" >  
        < div  class = " p-2 order-3 bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 order-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 order-1 bg-primary" >  Flex item 3</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.10 外边距  
在Bootstrap  5 中 ,  用于设置子元素外边距的类名及其介绍 : 
*  1.  . ms-auto :  设置子元素右外边距为auto ,  即 :  margin-right :  auto ! important ; . 
*  2.  . me-auto :  设置子元素左外边距为auto ,  即 :  margin-left :  auto ! important ; . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  外边距</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < div  class = " d-flex mb-3 bg-secondary" >  
        
        < div  class = " p-2 ms-auto bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        < div  class = " p-2 bg-primary" >  Flex item 3</ div>  
    </ div>  
    < div  class = " d-flex mb-3 bg-secondary" >  
        < div  class = " p-2  bg-info" >  Flex item 1</ div>  
        < div  class = " p-2 bg-warning" >  Flex item 2</ div>  
        
        < div  class = " p-2 me-auto bg-primary" >  Flex item 3</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.11 换行方式  
在  Bootstrap  5 中 ,  用于设置弹性容器的换行方式的相关类名及其介绍 : 
*  1.  . flex-nowrap :  默认 ,  弹性容器的子元素将会在一行内保持水平排列 ,  不会自动换行到下一行 . 
*  2.  . flex-wrap :   用于将弹性容器的子元素布局在单行或多行上 ,  以适应可用空间 .  
*  3.  . flex-wrap-reverse  类用于将弹性容器的子元素布局在反向的多行上。也就是说 ,  它会从下到上依次排列子元素。 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  换行</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < p> < code>  .flex-nowrap:</ code> </ p>  
    < div  class = " d-flex flex-nowrap bg-light" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
        < div  class = " p-2 border" >  Flex item 4</ div>  
        < div  class = " p-2 border" >  Flex item 5</ div>  
        < div  class = " p-2 border" >  Flex item 6</ div>  
        < div  class = " p-2 border" >  Flex item 7</ div>  
        < div  class = " p-2 border" >  Flex item 8</ div>  
        < div  class = " p-2 border" >  Flex item 9</ div>  
        < div  class = " p-2 border" >  Flex item 10</ div>  
    </ div>  
    < br>  
    < p> < code>  .flex-wrap:</ code> </ p>  
    < div  class = " d-flex flex-wrap bg-light" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
        < div  class = " p-2 border" >  Flex item 4</ div>  
        < div  class = " p-2 border" >  Flex item 5</ div>  
        < div  class = " p-2 border" >  Flex item 6</ div>  
        < div  class = " p-2 border" >  Flex item 7</ div>  
        < div  class = " p-2 border" >  Flex item 8</ div>  
        < div  class = " p-2 border" >  Flex item 9</ div>  
        < div  class = " p-2 border" >  Flex item 10</ div>  
    </ div>  
    < br>  
    < p> < code>  .flex-wrap-reverse:</ code> </ p>  
    < div  class = " d-flex flex-wrap-reverse bg-light" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
        < div  class = " p-2 border" >  Flex item 4</ div>  
        < div  class = " p-2 border" >  Flex item 5</ div>  
        < div  class = " p-2 border" >  Flex item 6</ div>  
        < div  class = " p-2 border" >  Flex item 7</ div>  
        < div  class = " p-2 border" >  Flex item 8</ div>  
        < div  class = " p-2 border" >  Flex item 9</ div>  
        < div  class = " p-2 border" >  Flex item 10</ div>  
    </ div>  
</ div>  
</ body>  
</ html>  
  
 
 7.12 内容对齐  
在  Bootstrap  5 中 ,  可以使用 . align-content- * 类来控制弹性容器中子元素在垂直方向上的堆叠方式 . 
相关类名及其介绍 : 
*  1.  . align-content-start :    默认 ,  子元素堆叠在垂直方向上的起始位置 . 
*  2.  . align-content-center :  子元素在垂直方向上居中对齐。 
*  3.  . align-content-end :     子元素堆叠在垂直方向上的结束位置 . 
*  4.  . align-content-between : 子元素均匀分布在垂直方向上 ,  两端贴紧容器边界 . 
*  5.  . align-content-around :  子元素均匀分布在垂直方向上 ,  各元素之间有空隙 . 
*  6.  . align-content-stretch : 子元素在垂直方向上拉伸以填满整个容器 . 
*  这些类在只有一行的弹性子元素中是无效的 ,  需要搭配flex-wrap或flex-wrap-reverse类使用 ,  也可以说它说多行内容的对齐方法 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  内容对齐</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < p>  .align-content-start (默认):</ p>  
    < div  class = " d-flex flex-wrap align-content-start bg-light"   style = " height : 100px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
        < div  class = " p-2 border" >  Flex item 4</ div>  
        < div  class = " p-2 border" >  Flex item 5</ div>  
        < div  class = " p-2 border" >  Flex item 6</ div>  
        < div  class = " p-2 border" >  Flex item 7</ div>  
        < div  class = " p-2 border" >  Flex item 8</ div>  
        < div  class = " p-2 border" >  Flex item 9</ div>  
        < div  class = " p-2 border" >  Flex item 10</ div>  
    </ div>  
    < br>  
    < p>  .align-content-center:</ p>  
    < div  class = " d-flex flex-wrap align-content-center bg-light"   style = " height : 100px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
        < div  class = " p-2 border" >  Flex item 4</ div>  
        < div  class = " p-2 border" >  Flex item 5</ div>  
        < div  class = " p-2 border" >  Flex item 6</ div>  
        < div  class = " p-2 border" >  Flex item 7</ div>  
        < div  class = " p-2 border" >  Flex item 8</ div>  
        < div  class = " p-2 border" >  Flex item 9</ div>  
        < div  class = " p-2 border" >  Flex item 10</ div>  
    </ div>  
    < br>  
    < p>  .align-content-end:</ p>  
    < div  class = " d-flex flex-wrap align-content-end bg-light"   style = " height : 100px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
        < div  class = " p-2 border" >  Flex item 4</ div>  
        < div  class = " p-2 border" >  Flex item 5</ div>  
        < div  class = " p-2 border" >  Flex item 6</ div>  
        < div  class = " p-2 border" >  Flex item 7</ div>  
        < div  class = " p-2 border" >  Flex item 8</ div>  
        < div  class = " p-2 border" >  Flex item 9</ div>  
        < div  class = " p-2 border" >  Flex item 10</ div>  
    </ div>  
    < br>  
    < p>  .align-content-around:</ p>  
    < div  class = " d-flex flex-wrap align-content-around bg-light"   style = " height : 300px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
        < div  class = " p-2 border" >  Flex item 4</ div>  
        < div  class = " p-2 border" >  Flex item 5</ div>  
        < div  class = " p-2 border" >  Flex item 6</ div>  
        < div  class = " p-2 border" >  Flex item 7</ div>  
        < div  class = " p-2 border" >  Flex item 8</ div>  
        < div  class = " p-2 border" >  Flex item 9</ div>  
        < div  class = " p-2 border" >  Flex item 10</ div>  
        < div  class = " p-2 border" >  Flex item 11</ div>  
        < div  class = " p-2 border" >  Flex item 12</ div>  
        < div  class = " p-2 border" >  Flex item 13</ div>  
        < div  class = " p-2 border" >  Flex item 14</ div>  
        < div  class = " p-2 border" >  Flex item 15</ div>  
        < div  class = " p-2 border" >  Flex item 16</ div>  
        < div  class = " p-2 border" >  Flex item 17</ div>  
        < div  class = " p-2 border" >  Flex item 18</ div>  
        < div  class = " p-2 border" >  Flex item 19</ div>  
        < div  class = " p-2 border" >  Flex item 20</ div>  
        < div  class = " p-2 border" >  Flex item 21</ div>  
        < div  class = " p-2 border" >  Flex item 22</ div>  
        < div  class = " p-2 border" >  Flex item 23</ div>  
        < div  class = " p-2 border" >  Flex item 24</ div>  
        < div  class = " p-2 border" >  Flex item 25</ div>  
    </ div>  
    < br>  
    < p>  .align-content-stretch:</ p>  
    < div  class = " d-flex flex-wrap align-content-stretch bg-light"   style = " height : 300px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
        < div  class = " p-2 border" >  Flex item 4</ div>  
        < div  class = " p-2 border" >  Flex item 5</ div>  
        < div  class = " p-2 border" >  Flex item 6</ div>  
        < div  class = " p-2 border" >  Flex item 7</ div>  
        < div  class = " p-2 border" >  Flex item 8</ div>  
        < div  class = " p-2 border" >  Flex item 9</ div>  
        < div  class = " p-2 border" >  Flex item 10</ div>  
            < div  class = " p-2 border" >  Flex item 11</ div>  
    < div  class = " p-2 border" >  Flex item 12</ div>  
    < div  class = " p-2 border" >  Flex item 13 </ div>  
    < div  class = " p-2 border" >  Flex item 14</ div>  
    < div  class = " p-2 border" >  Flex item 15</ div>  
    < div  class = " p-2 border" >  Flex item 16</ div>  
    < div  class = " p-2 border" >  Flex item 17</ div>  
    < div  class = " p-2 border" >  Flex item 18</ div>  
    < div  class = " p-2 border" >  Flex item 19</ div>  
    < div  class = " p-2 border" >  Flex item 20</ div>  
    < div  class = " p-2 border" >  Flex item 21</ div>  
    < div  class = " p-2 border" >  Flex item 22</ div>  
    < div  class = " p-2 border" >  Flex item 23</ div>  
    < div  class = " p-2 border" >  Flex item 24</ div>  
    < div  class = " p-2 border" >  Flex item 25</ div>  
    </ div>  
    < br>  
</ div>  
</ body>  
</ html>  
  
 
 7.13 子元素对齐  
在Bootstrap  5 中 ,  . align-items- * 类来控制弹性容器中的子元素在单行中的垂直对齐方式 . 
相关类名及其介绍 : 
*  1.  . align-items-start :  子元素在单行中垂直对齐的起始位置 . 
*  2.  . align-items-center:子元素在单行中垂直居中对齐 . 
*  3.  . align-items-end :  子元素在单行中垂直对齐的结束位置 . 
*  4.  . align-items-baseline:子元素在单行中以基线对齐 . 
*  5.  . align-items-stretch:子元素在单行中拉伸以填充垂直空间 ,  默认值。 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  子元素对齐</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < p>  .align-items-start:</ p>  
    < div  class = " d-flex align-items-start bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
    < p>  .align-items-center:</ p>  
    < div  class = " d-flex align-items-center bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
    < p>  .align-items-end:</ p>  
    < div  class = " d-flex align-items-end bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
    < p>  .align-items-baseline:</ p>  
    < div  class = " d-flex align-items-baseline bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
    < p>  .align-items-stretch (默认):</ p>  
    < div  class = " d-flex align-items-stretch bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
</ div>  
</ body>  
</ html>  
  
 
 7.14 指定子元素对齐  
在  Bootstrap  5 中 ,  可以使用 . align-self- * 类单独控制特定子元素的对齐方式 . 
相关类名及其介绍 : 
*  1.  . align-self-start :  将特定子元素垂直对齐到起始位置 . 
*  2.  . align-self-center :  将特定子元素垂直居中对齐 . 
*  3.  . align-self-end :  将特定子元素垂直对齐到结束位置 . 
*  4.  . align-self-baseline :  将特定子元素以基线对齐 . 
*  5.  . align-self-stretch :  将特定子元素拉伸以填充垂直空间 ,  这是默认值 . 
  
<! DOCTYPE  html >  
< html  lang = " en" >  
< head>  
    < meta  charset = " UTF-8" >  
    < meta  name = " viewport"   content = " width=device-width, initial-scale=1" >  
    < title>  指定子元素对齐</ title>  
    < link  href = " bootstrap-5.3.2-dist/css/bootstrap.min.css"   rel = " stylesheet" >  
    < script  src = " bootstrap-5.3.2-dist/js/bootstrap.bundle.min.js" > </ script>  
</ head>  
< body>  
< div  class = " container mt-3" >  
    < p>  .align-self-start:</ p>  
    < div  class = " d-flex bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border align-self-start" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
    < p>  .align-self-center:</ p>  
    < div  class = " d-flex bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border align-self-center" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
    < p>  .align-self-end:</ p>  
    < div  class = " d-flex bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border align-self-end" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
    < p>  .align-self-baseline:</ p>  
    < div  class = " d-flex bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border align-self-baseline" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
    < p>  .align-self-stretch (默认):</ p>  
    < div  class = " d-flex bg-light"   style = " height : 150px" >  
        < div  class = " p-2 border" >  Flex item 1</ div>  
        < div  class = " p-2 border align-self-stretch" >  Flex item 2</ div>  
        < div  class = " p-2 border" >  Flex item 3</ div>  
    </ div>  
    < br>  
</ div>  
</ body>  
</ html>  
  
 
 7.15 响应式flex类  
方向 : 
. flex- * -row 	                根据不同的屏幕设备在水平方向显示弹性子元素 . 
. flex- * -row-reverse 	        根据不同的屏幕设备在水平方向显示弹性子元素 . 
. flex- * -column 	            根据不同的屏幕设备在垂直方向显示弹性子元素 . 
. flex- * -column-reverse 	    根据不同的屏幕设备在垂直方向显示弹性子元素 ,  且方向相反 . 
内容对齐 : 
. justify-content- * -start 	根据不同屏幕设备在开始位置显示弹性子元素 ( 左对齐 ) . 
. justify-content- * -end 	    根据不同屏幕设备在尾部显示弹性子元素 ( 右对齐 ) . 	
. justify-content- * -center 	根据不同屏幕设备在flex容器中居中显示子元素 . 
. justify-content- * -between 	根据不同屏幕设备使用 "between" 显示弹性子元素 . 
. justify-content- * -around 	根据不同屏幕设备使用 "around" 显示弹性子元素 . 
等宽 : 
. flex- * -fill 	            根据不同的屏幕设备强制等宽 . 
扩展 : 
. flex- * -grow- 0 	            不同的屏幕设备不设置扩展 . 	 
. flex- * -grow- 1 	            不同的屏幕设备设置扩展 . 
换行方式 : 
. flex- * -nowrap 	            不同的屏幕设备不设置包裹元素 . 	
. flex- * -wrap 	            不同的屏幕设备设置包裹元素 . 	
. flex- * -wrap-reverse 	    不同的屏幕设备反转包裹元素 . 
内容排列 : 
. align-content- * -start 	    根据不同屏幕设备在起始位置堆叠元素 . 	
. align-content- * -end 	    根据不同屏幕设备在结束位置堆叠元素 . 
. align-content- * -center 	    根据不同屏幕设备在中间位置堆叠元素 . 	
. align-content- * -around 	    根据不同屏幕设备 ,  使用 "around" 堆叠元素 . 	
. align-content- * -stretch 	根据不同屏幕设备 ,  通过伸展元素来堆叠 . 
排序 : 
. order- * - 0 - 12 	            根据不同屏幕设备 ,  修改子元素的排序 . 
元素对齐 : 
. align-items- * -start 	    根据不同屏幕设备 ,  让元素在头部显示在同一行 . 
. align-items- * -end 	        根据不同屏幕设备 ,  让元素在尾部显示在同一行 . 
. align-items- * -center 	    根据不同屏幕设备 ,  让元素在中间位置显示在同一行 . 
. align-items- * -baseline 	    根据不同屏幕设备 ,  让元素在基线上显示在同一行 . 
. align-items- * -stretch 	    根据不同屏幕设备 ,  让元素延展高度并显示在同一行 . 
单独一个子元素的对齐方式 : 
. align-self- * -start 	        据不同屏幕设备 ,  让单独一个子元素显示在头部 . 
. align-self- * -end 	        据不同屏幕设备 ,  让单独一个子元素显示在尾部 . 	
. align-self- * -center 	    据不同屏幕设备 ,  让单独一个子元素显示在居中位置 . 	
. align-self- * -baseline 	    据不同屏幕设备 ,  让单独一个子元素显示在基线位置 . 	
. align-self- * -stretch 	    据不同屏幕设备 ,  延展一个单独子元素 .