你能实现多少种水平垂直居中的布局？

1、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>

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、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>