Z index

I made something a while ago with but after doing corrections on that column, things moved.
i need the green column behind so that it looks like this. image

i put in the css for the green box: .green-box
{margin-top: -150px: z-index:-1; padding-bottom: 50px;} and it worked.

I only changed the text in the box not the css i cant think why it changed to this: image
how to do i get it back?

oops i see my mistake. it has colon instead of semi colon