一、绝对定位 + margin,让固定宽高的盒子水平垂直居中于窗口
<!DOCTYPE>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1.0" >
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<style>
.wangyi-loading{
width: 360px;
height: 360px;
margin:auto;
position: absolute;
top:0;
right:0;
bottom:0;
left:0;
border:5px solid red;
}
</style>
</head>
<body>
<div class="wangyi-loading"></div>
</body>
</html>
二、 绝对定位+transform:translate() ,让盒子水平垂直居中于窗口
<!DOCTYPE>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1.0" >
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<style>
.son{
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%,-50%);
border:5px solid lightcoral;
}
</style>
</head>
<body>
<div class="son"> 我是居中的盒子</div>
</body>
</html>
三、父级用flex布局 ,让盒子水平垂直居中于窗口
<!DOCTYPE>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1.0" >
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<style>
.father{
display: flex;
align-items: center;
justify-content: center;
border:2px solid green;
height:100vh;
}
.son{
border:5px solid lightcoral;
}
</style>
</head>
<body>
<div class="father">
<div class="son">
盒子居中
</div>
</div>
</body>
</html>
四 、父级flex布局 + 子级margin:auto,让盒子水平垂直居中于窗口
<!DOCTYPE>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1.0" >
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<style>
.father{
display: flex;
border:2px solid green;
height:100vh;
}
.son{
border:5px solid lightcoral;
margin: auto;
}
</style>
</head>
<body>
<div class="father">
<div class="son">我就是那个居中的盒子</div>
</div>
</body>
</html>
五 、父级display: table-cell + 子级margin:0 auto,让盒子水平垂直居中于窗口
<!DOCTYPE>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1.0" >
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<style>
.father{
display: table-cell;
vertical-align: middle;
border:2px solid green;
height:100vh;
width: 100vw;
}
.son{
border:5px solid lightcoral;
width: 200px;
margin: 0 auto;
}
</style>
</head>
<body>
<div class="father">
<div class="son">我就是那个居中的盒子</div>
</div>
</body>
</html>
六 、父级网格布局display:grid + 子级grid-area指定项目位置,让盒子水平垂直居中于窗口
<!DOCTYPE>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<style>
.father {
display: grid;
grid-template-rows: 1fr 100px 1fr;
grid-template-columns: 1fr 100px 1fr;
border: 2px solid green;
height: 100vh;
width: 100vw;
}
.son {
border: 5px solid lightcoral;
grid-area: 2/2/3/3;
}
</style>
</head>
<body>
<div class="father">
<div class="son">我就是那个居中的盒子</div>
</div>
</body>
</html>

关于
网格布局的更多信息,可参考:
CSS Grid 网格布局教程