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布局

布局是 CSS 知识体系的重中之重

布局又称为版式布局，是网页UI设计师将有限的视觉元素进行有机的排列组合

早期以 table 为主(简单)
后来以技巧性布局为主(难)
现在有flexbox/grid(偏简单)
响应式布局是必备知识

常用布局方法：
table表格布局
float浮动+margin
inline-block布局
flexbox布局(正统布局方式)

div 块独占一行
float 

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<div class="div1">div1</div>
<div class="div2">div2</div>
<div class="div3">div3</div>
<div class="div4">div4</div>
<div class="div5">div5</div>
<div class="div6">div6</div>

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div {
    width: 300px;
    height: 300px;
    border: 1px solid black;
    /* float: left; */
    background: greenyellow;
}
.div1, .div2 {
    float: left;
    background: red;
    width: 150px;
    height: 100px;
}
.div3 {
    clear: both;
}

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div {
    width: 300px;
    height: 300px;
    border: 1px solid black;
    /* float: left; */
    background: greenyellow;
}
.div1, .div2 {
    float: left;
    background: red;
    width: 150px;
    height: 100px;
}
.div3 {
    clear: both;
}
.div4 {
    float: right;
    background: blue;
    width: 150px;
    height: 100px;
}
.div5 {
    clear: both;
}

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<div class="container">
    <div class="div1">div1</div>
    <div class="div2">div2</div>
    <div class="div3">div3</div>
    <div class="div4">div4</div>
    <div class="div5">div5</div>
</div>

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div {
    border: 1px solid black;
    background: greenyellow;
}
.div1, .div2, .div3, .div4, .div5 {
    float: left;
    background: red;
    width: 200px;
    height: 200px;
}
/* 伪元素 是一个行元素 清理浮动*/
.container::after {
    content: " ";
    /* 变成块元素 */
    display: block;
    clear: both;
}

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div {
    /* border: 1px solid black; */
    background: greenyellow;
    margin: 20px;
}
.div1 {
    width: 200px;
    height: 200px;
    background: green;
}
.div2, .div3, .div4, .div5 {
    float: left;
    background: red;
    width: 200px;
    height: 200px;
}
/* 伪元素 是一个行元素 清理浮动*/
/* .container::after {
    content: " "; */
    /* 变成块元素 */
    /* display: block;
    clear: both;
} */
/* 伪元素 清理浮动和 margin */
.container::before, .container::after {
    content: "";
    display: table;

}
.container::after {
    clear: both;
}

一列布局

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<!DOCTYPE html>
<html lang="zh">
<head>
  <meta charset="UTF-8">
  <title>一列布局</title>
  <style>
    body { margin: 0; padding: 0; }
    .top {
      height: 100px;
      background: blue;
    }
    .main {
      width: 800px;
      height: 300px;
      background: #ccc;
      margin: 0 auto;
    }
    .foot {
      width: 800px;
      height: 100px;
      background: #900;
      margin: 0 auto;
    }
  </style>
</head>
<body>
  <div class="top"></div>
  <div class="main"></div>
  <div class="foot"></div>
</body>
</html>

两列布局

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<!DOCTYPE html>
<html lang="zh">
<head>
  <meta charset="UTF-8">
  <title>两列布局</title>
  <style>
    body { margin: 0; padding: 0; }
    .main {
      width: 800px;
      margin: 0 auto;
    }
    .left {
      width: 20%;
      height: 500px;
      float: left;
      background: #ccc;
    }
    .right {
      width: 80%;
      height: 500px;
      float: right;
      background: #ddd;
    }
  </style>
</head>
<body>
  <div class="main">
    <div class="left"></div>
    <div class="right"></div>
  </div>
</body>
</html>

三列布局

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<!DOCTYPE html>
<html lang="zh">
<head>
  <meta charset="UTF-8">
  <title>两列布局</title>
  <style>
    body { margin: 0; padding: 0; }
    .left {
      width: 200px;
      height: 500px;
      background: #ccc;
      position: absolute;
      left: 0;
      top: 0;
    }
    .middle {
      height: 500px;
      background: #999;
      margin: 0 310px 0 210px
    }
    .right {
      width: 300px;
      height: 500px;
      background: #ddd;
      position: absolute;
      right: 0;
      top: 0;
    }
  </style>
</head>
<body>
  <div class="left">200px</div>
  <div class="middle">中间</div>
  <div class="right">300px</div>
</body>
</html>

混合布局

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<!DOCTYPE html>
<html lang="zh">
<head>
  <meta charset="UTF-8">
  <title>混合布局</title>
  <style>
    body { margin: 0; padding: 0; }
    .top {
      height: 100px;
      background: blue;
    }
    .head {
      height: 100px;
      width: 800px;
      background: #f60;
      margin: 0 auto;
    }
    .main {
      width: 800px;
      height: 600px;
      background: #ccc;
      margin: 0 auto;
    }
    .left {
      width: 200px;
      height: 600px;
      float: left;
      background: yellow;
    }
    .right {
      width: 600px;
      height: 600px;
      float: right;
      background: #369;
    }
    .sub_l {
      width: 400px;
      height: 600px;
      float: left;
      background: green;
    }
    .sub_r {
      width: 200px;
      height: 600px;
      float: right;
      background: #09F;
    }
    .foot {
      width: 800px;
      height: 100px;
      background: #900;
      margin: 0 auto;
    }
  </style>
</head>
<body>
  <div class="top">
    <div class="head"></div>
  </div>
  <div class="main">
    <div class="left"></div>
    <div class="right">
      <div class="sub_l"></div>
      <div class="sub_r"></div>
    </div>
  </div>
  <div class="foot"></div>
</body>
</html>

float

元素“浮动”；脱离文档流，但不脱离文本流

对自身的影响：形成“块”(BFC)；位置尽量靠上；

对兄弟的影响：上面贴非float元素；旁边贴float元素；不影响其它块级元素位置；影响其它块级元素内部文本

对父级元素的影响；从布局上“消失”；高度塌陷；

flexbox

弹性盒子

盒子本来就是并列的

指定宽度即可

display: flex

flex: 1

inline-block

像文本一样排block元素；没有清除浮动等问题；需要处理间隙