**绝对定位居中：**
.centered {
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
}
**水平居中：**
.h-center {
position: absolute;
left: 50%;
transform: translateX(-50%);
}
**全屏覆盖：**
.overlay {
position: fixed;
top: 0;
left: 0;
right: 0;
bottom: 0;
/* 或者 inset: 0; */
}
