第一种：给父级设置宽高100%，div设置绝对定位，left,right,top,bottom设置为0，margin：auto即可实现
//布局 style
*{
margin: 0;
padding: 0;
}
body,html{
width: 100%;
height: 100%;
position: relative;
}
.div{
position: absolute;
width: 200px;
height: 200px;
background: salmon;
left: 0;
right: 0;
top: 0;
bottom: 0;
margin: auto;
}
//body
<body>
<div class="div"></div>
</body>
第二种：利用绝对定位和tranform（过渡动画）实现，div绝对定位，left: 50%; top: 50%;然后设置 transform: translate3d(-50%,-50%,0);即可
<style>
*{
margin: 0;
padding: 0;
}
body,html{
width: 100%;
height: 100%;
position: relative;
}
.div{
position: absolute;
width: 200px;
height: 200px;
background: salmon;
left: 50%;
top: 50%;
transform: translate3d(-50%,-50%,0);
}
</style>
//body
<body>
<div class="div"></div>
</body>
第三种：flex弹性盒布局，给父级div设置display:flex,设置水平和垂直居中 justify-content: center; align-items: center;
//style
.div{
width: 100%;
height: 100%;
display: flex;
justify-content: center;
align-items: center;
}
.box{
width: 200px;
height: 200px;
background: sandybrown;
}
//body
<body>
<div class="div">
<div class="box"></div>
</div>
</body>
第四种：div设置绝对定位，left: 50%; top: 50%距离左和上是margin-left：calc(-div自身宽度/2),margin-top:calc(-div自身高度/2)，也可以自己计算margin-left和margin-top的值
//style
<style>
*{
margin: 0;
padding: 0;
}
body,html{
width: 100%;
height: 100%;
position: relative;
}
.div{
position: absolute;
width: 200px;
height: 200px;
background: salmon;
left: 50%;
top: 50%;
margin-left:calc(-200px/2);
margin-top: calc(-200px/2);
}
</style>
//body
<div class="div">
<div class="box"></div>
</div>
以上就是四种方法的实现
有不对的请指教~
