我们在日常的开发中，经常会遇到这样一个问题，就是如何实现居中水平垂直居中对齐。并且在面试中也会出现这样的问题，但是我们往往回答的不是很全部，而导致没有得到面试加分。接下来我们通过不同的方式来实现，让我们成功破解这道面试。

定宽高

一、绝对定位和负magin值

   <template>
   <div id="app">
     <div class="box">
        <div class="children-box"></div>
     </div> 
   </div> 
   </template>
   <style type="text/css"> 
   .box {
        width: 200px; 
        height: 200px; 
        border: 1px solid red; 
        position: relative; 
        }
   .children-box{ 
         position: absolute; 
         width: 100px; height: 100px; 
         background: yellow; 
         left: 50%; 
         top: 50%; 
         margin-left: -50px; 
         margin-top: -50px; 
         } 
   </style>

二、绝对定位 + transform

  <template>
    <div id="app">
        <div class="box">
            <div class="children-box"></div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    position: relative;
}
.children-box {
    position: absolute;
    width: 100px;
    height: 100px;
    background: yellow;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%); 
}
</style>

三、绝对定位 + left/right/bottom/top + margin

<template>
    <div id="app">
        <div class="box">
            <div class="children-box"></div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    position: relative;
}
.children-box {
    position: absolute;
    display: inline;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0px;
    background: yellow;
    margin: auto;
    height: 100px;
    width: 100px;
}
</style>

四、flex布局

<template>
    <div id="app">
        <div class="box">
            <div class="children-box"></div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    display: flex;
    justify-content: center;
    align-items: center;
}
.children-box {
    background: yellow;
    height: 100px;
    width: 100px;
}
</style>

五、grid布局

<template>
    <div id="app">
        <div class="box">
            <div class="children-box"></div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    display: grid;
}
.children-box {
    width: 100px;
    height: 100px;
    background: yellow;
    margin: auto;
}
</style>

六、table-cell + vertical-align + inline-block/margin: auto

<template>
    <div id="app">
        <div class="box">
            <div class="children-box"></div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    display: table-cell;
    text-align: center;
    vertical-align: middle;
}
.children-box {
    width: 100px;
    height: 100px;
    background: yellow;
    display: inline-block;// 可以换成margin: auto;
}
</style>

2、不定宽高

一、绝对定位 + transform

<template>
    <div id="app">
        <div class="box">
            <div class="children-box">111111</div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    position: relative;
}
.children-box {
   position: absolute;
   background: yellow;
   left: 50%;
   top: 50%;
   transform: translate(-50%, -50%);
}
</style>

二、table-cell

<template>
    <div id="app">
        <div class="box">
            <div class="children-box">111111</div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    display: table-cell;
    text-align: center;
    vertical-align: middle;
}
.children-box {
   background: yellow;
   display: inline-block;
}
</style>

三、flex布局

<template>
    <div id="app">
        <div class="box">
            <div class="children-box">11111111</div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    display: flex;
    justify-content: center;
    align-items: center;
}
.children-box {
    background: yellow;
}
</style>

四、flex变异布局

<template>
    <div id="app">
        <div class="box">
            <div class="children-box">11111111</div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    display: flex;
}
.children-box {
    background: yellow;
    margin: auto;
}
</style>

五、grid + flex布局

<template>
    <div id="app">
        <div class="box">
            <div class="children-box">11111111</div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    display: grid;
}
.children-box {
    background: yellow;
    align-self: center;
    justify-self: center;
}
</style>

六、gird + margin布局

<template>
    <div id="app">
        <div class="box">
            <div class="children-box">11111111</div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    display: grid;
}
.children-box {
    background: yellow;
    margin: auto;
}
</style>

七、writing-mode属性布局

<template>
    <div id="app">
        <div class="box">
            <div class="children-box">
                <p>11111</p>
            </div>
        </div>
    </div>
</template>
<style type="text/css">
.box {
    width: 200px;
    height: 200px;
    border: 1px solid red;
    writing-mode: vertical-lr;
    text-align: center;
}

.box>.children-box {
    writing-mode: horizontal-tb;
    display: inline-block;
    text-align: center;
    width: 100%;
}

.box>.children-box>p {
    display: inline-block;
    margin: auto;
    text-align: left;
    background: yellow;
}
</style>