Div Layer Alignment

[leevg]

Im creating the layout for a website using div. On the right hand side I have a flex application which is a login and registration screen. When the user clicks registration the application changes size within the div. I set the Z-index to overlap so it would expand over top of the current layout, but it expands left, which is off of my page and I want it to expand and overlap to the right.

Does that make any sense? Ive been looking for answers but I can't seem to find any. I guess the default position is the top left corner so it expands from there. Any suggestions?

-Lee