How do I make my pop up appear in a certain position?

Here is my CSS code:

.wdpu-msg-inner .wdpu-text {
padding: 0;
}

.wdpu-msg {
position: absolute;
top: 20px;
right: -500px;
}

The right position is working, but no matter what I set the top number to, it positions itself half way down the page. For some users running a lower resolution, only 1/2 the pop up appears because it's too far down the screen.

Thank you.