Child Theme Creation On Already Modified Site

Hi,

I downloaded a premium theme and started to make edits such as backgrounds, menus etc….

I then read that I should really be doing this through a child theme. I therefore created a child theme and started by referencing the style.css file back to the parent folder.

When I activated the child theme however, all of the changes I had made to the parent theme disappeared. I then reactivated the parent theme, and they all came back.

My question is why is this happening? Shouldn’t the changes I have already made be reflected in the parent theme style.css and therefore should appear when I activate the child theme given this is just referencing the parent theme style.css?

Many thanks for your help.