How to set the registration form in the center of the site?

Question

css

I think if I use
margin:auto;
witdh:xxpx;
then at different screen sizes it will be askew, I have not yet encountered such a task, I have already read it in Habré, it does not help.

this block is right in the middle

Answer 1

display:flex;
justify-content:center;
align-items:center;

Answer 2

There is another option without flex:

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

Also specify the width and height respectively.