面试中的CSS（二）--三列布局，左右定宽中间自适应

1.绝对定位 + margin

<div class="parent">
  <div class="left"></div>
  <div class="main"></div>
  <div class="right"></div>
</div>

.parent {
  position: relative;
}
.left, .right {
  width: 200px;
}
.left {
  position: absolute;
  left: 0;
  top: 0;
}
.right {
  position: absolute;
  right: 0;
  top: 0;
}
.main {
  margin: auto 200px;
}

2.float

注意： 左右两边的float脱离了文档流，所以main一定要写在最后

<div class="parent">
  <div class="left"></div>
  <div class="right"></div>
  <div class="main"></div>
</div>

3.flex大法好

<div class="parent">
  <div class="left"></div>
  <div class="main"></div>
  <div class="right"></div>
</div>

.parent {
  display: flex;
  justify-content: space-between;
}
.left, .right {
  width: 200px;
}
.main {
  flex: 1;
}