单列布局

实现方式： 定宽+水平居中

width: 1000px; //或 max-width: 1000px;
margin-left: auto;
margin-right: auto;

max-width和width的区别:固定宽度当浏览器缩小时页面出现滚动条；最大宽度当页面缩小时页面自动伸缩 以真实宽度作为浏览器计算的基准
1.一栏布局

<style>
  .layout{
  /*   width: 960px; */
    max-width: 960px;
    margin: 0 auto;
  }
  #header{
    height: 60px;
    background: red;
  }
  #content{
    height: 400px;
    background: blue;
  }
  #footer{
    height: 50px;
    background: yellow;
  }
</style>
<div class="layout">
  <div id="header">头部</div>
  <div id="content">内容</div>
  <div id="footer">尾部</div>
</div>

也可有如下写法，省标签，便于控制局部:

<style>
  .layout{
    width: 960px;
    margin: 0 auto;
  }
  #header{
    height: 60px;
    background: red;
  }
  #content{
    height: 400px;
    background: blue;
  }
  #footer{
    height: 50px;
    background: yellow;
  }
</style>
<div id="header"  class="layout">头部</div>
<div id="content" class="layout">内容</div>
<div id="footer" class="layout">尾部</div>

2.通栏布局

<style>
  .layout{
    width: 960px;
    margin: 0 auto;
  }
  body{
    min-width: 960px;
  }
  #header{
    height: 60px;
    background: red;
  }
  #content{
    height: 400px;
    background: blue;
  }
  #footer{
    height: 50px;
    background: yellow;
  }
</style>
<div id="header">
  <div class="layout">头部</div>
</div>
<div id="content" class="layout">内容</div>
<div id="footer">
  <div class="layout">尾部</div>
</div>

双列布局

浮动元素+普通元素marmgin

<style>
    #content:after{
      content: '';
      display: block;
      clear: both;
    }
    .aside{
      width: 200px;
      height: 500px;
      background: yellow;
      float: left;
    }
    .main{
      margin-left: 210px;
      height: 400px;
      background: red;
    }

    #footer{
      background: #ccc;
    }

  </style>
  <div id="content">
    <div class="aside">aside</div>
    <div class="main">content</div>
  </div>
  <div id="footer">footer</div>

三列布局

两侧两列固定宽度，中间列自适应宽度

#content:after{
      content: '';
      display: block;
      clear: both;
    }
    .menu{
      width: 100px;
      height: 500px;
      background: pink;
      float: left;
    }
    .aside{
      width: 200px;
      height: 500px;
      background: yellow;
      float: right;
    }
    .main{
      margin-left: 110px; /*为什么要加margin-left*/
      margin-right: 210px;
      height: 400px;
      background: red;
    }

    #footer{
      background: #ccc;
    }

  <div id="content">
    <!-- 为什么不是main在前面 -->
    <div class="menu">aside</div>
    <div class="aside">aside</div>
    <div class="main">content</div>
  </div>
  <div id="footer">footer</div>

水平等距排列

<style>
ul,li{
  margin: 0;
  padding: 0;
  list-style: none;
}
.ct{
    overflow:hidden;
    width: 640px;
    border:dashed 1px orange;
    margin: 0 auto;
}

.ct .item{
    float:left;
    margin-left: 20px;
    margin-top: 20px;
    width:200px;
    height:200px;
    background: red;
}
.ct>ul{
  margin-left: -20px;
}

</style>
<div class="ct">
  <ul>
    <li class="item">1</li>
    <li class="item">2</li>
    <li class="item">3</li>
    <li class="item">4</li>
    <li class="item">5</li>
    <li class="item">6</li>
    <li class="item">7</li>
    <li class="item">8</li>
  </ul>
</div>