块、行内块水平垂直居中

1.定位实现水平垂直居中

<div class="outer"><div class="test inner1">定位实现水平垂直居中</div></div><style>.outer {width: 300px;height: 300px;border: 1px solid gray;margin: 100px auto 0;position: relative;}.test {width: 100px;height: 100px;background-color: orange;}.inner1 {/* 方法一 定位*/position: absolute;/* 相对于包含块，最近的定位的祖先或父元素 */top: 50%; left: 50%;margin-left: -50px;margin-top: -50px;}
</style>

2.定位+位移

<div class="outer"><div class="test inner2">定位+位移</div></div>
<style>
.outer {width: 300px;height: 300px;border: 1px solid gray;margin: 100px auto 0;position: relative;}.test {width: 100px;height: 100px;background-color: orange;}.inner2 {position: absolute;top: 50%;left: 50%;/*方法二  translate中的百分比是相对自身，50% 相当于100*50% = 50*/transform: translate(-50%, -50%);}
</style>

3.相对于整个视口水平垂直居中

 <div class="view">相对于整个视口水平垂直居中</div><style>body {position: relative;}/* 方法三 */.view {width: 100px;height: 100px;background-image: linear-gradient(red, yellow, green);position: fixed;top: 0;left: 0;right: 0;bottom: 0;margin: auto;}</style>

4.遮挡层

<div class="item"></div>/* 遮挡层 */.item {background-image: repeating-linear-gradient(red 200px, yellow 500px, green 700px);opacity: 0.5;position: fixed;top: 0;left: 0;right: 0;bottom: 0; }