how do I center javascript css popup div, no matter what the screen resolution?

Question

I have the following code that opens a new popup window while disabling the background, the problem is that I have to position this so that it\'s 100px from the top (already got

Answer 1

Just do this:

.body {
    position: relative;
}
.popup {
    position: absolute;
    max-width: 800px;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

no matters the screen or popup size. This will center the

.