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绝对定位、固定定位及flex容器

1. 绝对定位与固定定位,并描述联系与区别

1.1 绝对定位absolute

HTML代码

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>绝对定位及相对定位</title>
  </head>
  <body>
    <ul>
      <li class="relative">相对定位</li>
      <li class="absolute">绝对定位</li>
    </ul>
    <style>
      * {
        margin: 0;
        padding: 0;
        box-sizing: border-box;
      }
      body {
        border: 5px solid red;
      }
      ul {
        width: 400px;
        height: 300px;
        border: 5px solid blue;
      }
      ul li {
        height: 40px;
        border: 1px solid black;
        list-style: none;
      }
      ul li:first-child {
        background-color: blue;
      }
      ul li:last-child {
        background-color: yellow;
      }
      ul li.absolute {
        position: absolute;
        top: 70px;
        left: 20px;
      }
      /* ul li.relative {
        position: relative;
        top: 10px;
        left: 100px;
      } */
    </style>
  </body>
</html>

页面演示效果：
绝对定位

1.2 相对定位

HTML代码

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>绝对定位及相对定位</title>
  </head>
  <body>
    <ul>
      <li class="relative">相对定位</li>
      <li class="absolute">绝对定位</li>
    </ul>
    <style>
      * {
        margin: 0;
        padding: 0;
        box-sizing: border-box;
      }
      body {
        border: 5px solid red;
      }
      ul {
        width: 400px;
        height: 300px;
        border: 5px solid blue;
      }
      ul li {
        height: 40px;
        border: 1px solid black;
        list-style: none;
      }
      ul li:first-child {
        background-color: blue;
      }
      ul li:last-child {
        background-color: yellow;
      }
      ul li.absolute {
        position: absolute;
        /* top: 70px; */
        /* left: 20px; */
      }
      ul li.relative {
        position: relative;
        top: 10px;
        left: 100px;
      }
    </style>
  </body>
</html>

页面演示效果如下：
相对定位

2.flex容器、容器属性及项目属性

2.1 容器：

初始html代码及页面演示效果：
html代码

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>flex布局及常用元素</title>
  </head>
  <body>
    <div class="container">
      <div class="item">item1</div>
      <div class="item">item2</div>
      <div class="item">item3</div>
    </div>
    <style>
      .container {
        display: flex;
        width: 500px;
        height: 60px;
        border: 1px solid black;
        flex-flow: row nowrap;
        place-content: start;
      }
      .container .item {
        width: 100px;
        height: 30px;
        background-color: lightgreen;
        border: 1px solid red;
        text-align: center;
      }
    </style>
  </body>
</html>

页面演示效果：

2.2容器属性

2.2.1 `place-content`: 项目在”主轴”上的排列方式

右端靠齐

.container {
     display: flex;
     width: 500px;
     height: 60px;
     border: 1px solid black;
     flex-flow: row nowrap;
     place-content: end;
   }

二端对齐

.container {
     display: flex;
     width: 500px;
     height: 60px;
     border: 1px solid black;
     flex-flow: row nowrap;
     place-content: space-between;
   }

分散对齐

.container {
     display: flex;
     width: 500px;
     height: 60px;
     border: 1px solid black;
     flex-flow: row nowrap;
     place-content: space-around;
   }

平均对齐

.container {
    display: flex;
    width: 500px;
    height: 60px;
    border: 1px solid black;
    flex-flow: row nowrap;
    place-content: space-evenly;
  }

2.2.2 `place-items`: 项目在”交叉轴”上的排列方式

顶部对齐

 .container {
     display: flex;
     width: 500px;
     height: 100px;
     border: 1px solid black;
     flex-flow: row nowrap;
     place-content: start;
     place-items: start;
   }

底部对齐

 .container {
     display: flex;
     width: 500px;
     height: 100px;
     border: 1px solid black;
     flex-flow: row nowrap;
     place-content: start;
     place-items: end;
   }

中间对齐

 .container {
     display: flex;
     width: 500px;
     height: 100px;
     border: 1px solid black;
     flex-flow: row nowrap;
     place-content: start;
     place-items: center;
   }

2.3 项目属性

2.3.1 `flex`: 项目在”主轴”上的缩放比例与宽度

flex: 放大比例允许收缩主轴空间

flexflex: 0 1 auto;默认,不放大,但可以自动收缩同flex:initial;

<style>
   .container {
     display: flex;
     width: 500px;
     /* height: 100px; */
     border: 1px solid black;
     flex-flow: row nowrap;
     place-content: start;
     place-items: center;
   }
   .container .item {
     width: 100px;
     height: 150px;
     background-color: lightgreen;
     border: 1px solid red;
     text-align: center;
     flex: 0 1 auto;
   }

flex: 1 1 auto;完全响应式,允许放大和自动收缩同flex:1;
flex: 0 0 auto;完全不响应同flex:none;

2.3.2 `place-self` 某项目在”交叉轴”上的排列方式

1 .place-self: start; 顶对齐

   .container > .item:nth-of-type(2) {
        background-color: yellow;
        height: 50px;
        place-self: start;
      }

2 . place-self: end; 底对齐

3 . place-self: center;中间对齐

2.3.3 `order`: 项目在”主轴”上的排列顺序

默认每个项目的order = 0,至越大，排序越靠后（值也可为负值）
例如：将item2 order设为3

 .container > .item:nth-of-type(2) {
        background-color: yellow;
        height: 50px;
        place-self: end;
        order: 3;
      }

批改老师：

PHPz

批改状态：合格

老师批语：作业完成的很细致

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