一、居中布局

<div class="parent" style="width:300px;height:300px;">
    <div class="child"> 居中布局 </div>
</div>

水平居中（宽度自适应）

1.inline-block + text-align

.child{display:inline-block;  /* 变成行内块元素，让元素宽度自适应，不继承父元素宽度；*/}
.parent{text-align: center;}

2.table + margin

.child{
    display: table;   /* 变成 table 元素，可以让元素宽度自适应，不继承父元素宽度；*/
    margin: 0 auto;  
}

3.absolute + transform

.parent{position: relative;}
.child{
    position: absolute;   /* 定位，可以让元素宽度自适应，不继承父元素宽度；*/
    transform: translateX(-50%);  
    left: 50%;
}

4.flex + justify-content

.parent{
    display: flex;
    justify-content: center;
}
/* 或者 */
.parent{display: flex;}
.child{margin: 0 auto;}

垂直居中（高度自适应）

1.table-cell + vertical-align

.parent{
    display: table-cell;  /* 变成类似 td 元素 */
    vertical-align: middle;
}

2.absolute + transform

.parent{position: relative;}
.child{
    position: absolute;   /* 定位，可以让元素宽度自适应，不继承父元素宽度；*/
    top: 50%;
    transform: translateY(-50%);
}

3.flex + align-items

.parent{
    display: flex;
    align-items: center;
}

水平垂直居中

1. inline-block + text-align + table-cell + vertical-align

.parent{
    text-align: center;
    display: table-cell;
    vertical-align: middle;
}
.child{display: inline-block;}

2.absolute + transform

.parent{position: relative;}
.child{
    position: absolute;   /* 定位，可以让元素宽度自适应，不继承父元素宽度；*/
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

3.flex + align-items + justify-content

.parent{
    display: flex;
    align-items: center;
    justify-content: center;
}

二、多列布局

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

左边定宽，右边自适应

1. float + margin

.left{
    width: 100px;
    float: left;
}
.right{margin-left: 120px;}

1. float + overflow

/* 和 1 方法表现的效果一样 */
.left{
    width: 100px;
    float: left;
}
.right{
    margin-left: 20px;
    overflow: hidden;
}

1. table

.parent{
    display: table;
    width: 100%;
    table-layout: fixed;
}
.left,.right{display: table-cell;}
.left{
    width: 100px;
    padding-right: 20px;
}

1. flex

.parent{display: flex;}
.right{flex: 1;}
.left{width: 100px;}

1. absolute

.parent{position: relative;}
.right{
    position: absolute;
    left: 100px;
    right: 0;
}
.left{width: 100px;}

左边不定宽，右边自适应

1. float + overflow

.left{float: left;}
.right{
    margin-left: 20px;
    overflow: hidden;
}

1. table

.parent{
    display: table;
    width: 100%;
}
.left,.right{display: table-cell;}
.left{width: 0.1%;}
.left{padding-left: 10px;}

1. flex

.parent{display: flex;}
.right{flex: 1;}
.left{margin-right: 20px;}

三、等宽布局

// 假如是 n 个 child
<div class="parent-fix">
    <div class="parent">
        <div class="child"><p>1</p></div>
        <div class="child"><p>2</p></div>
        <div class="child"><p>3</p></div>
        <div class="child"><p>4</p></div>
    </div>
</div>

1. table

.parent-fix{margin-left: -20px;}
.parent{
    display: table;
    width: 100%;
    table-layout: fixed;
}
.child{
    display: table-cell;
    padding-left: 20px;
}

1. flex

.parent{display: flex;}
.child{flex: 1;}
.child+.child {margin-left: 20px;}

四、等高布局

<div class="parent"  style="background: black;">
    <div class="left" style="background: red;">
        <p>left</p>
    </div>
    <div class="right" style="background: green;">
        <p>right</p>
        <p>right</p>
    </div>
</div>

1. table

.parent{
    display: table;
    width: 100%;
    table-layout: fixed;
}
.left,.right{display: table-cell;}
.left{
    width: 100px;
    border-right: 20px solid transparent;
    background-clip: padding-box;
}

1. flex

.parent{display: flex;}
.right{flex: 1;}
.left{
    width: 100px;
    margin-right: 20px;
}

1. float

// 部分 UI 框架采用的就是这种方式，.parent{overflow: hidden;}
.left{
    float: left;
    margin-right: 20px;
}
.right{overflow: hidden;}
.left,.right{
    padding-bottom: 9999px;
    margin-bottom: -9999px;
}