如何写一个遮挡层和对话框

1. 遮挡层，全屏
2. 对话框上下左右居中

html

<div class="wrapper">
    <div class="bg"></div>
    <div class="contaier"></div>
</div>

css

.wrapper, .bg {
    position: fixed;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    overflow-y: auto
}
.bg {
    background: #364252;
    opacity: 0.7;
}
.contaier {
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%,-50%);
    width: 600px;
    height: 500px;
    background-color: red;
}