实现水平垂直居中

1. flex 实现

.father {
    display: flex;
    justify-content: center;
    align-items: center;
}

2. 绝对定位配合 transform

.father {
    position: relative;
}
.son {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

3. 绝对定位配合 margin: auto;

.father {
    position: relative;
}
.son {
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    margin: auto;
}