I lost my "paper" color code

[MikeKReader]

I was playing about the other night and wrote some code in one of the books I was editing. Something like this:

body { color: rgb(255,255,255); /* text will be black */
background-color: rgb(255,255,200); /* the 'paper' the text is on will be a soft biege colour */
}

Played around with it and it seemed to work. I thought I wrote it in stylesheet.css (or whatever the standard stylesheet that shows up in every conversion is called). I thought I also wrote created a separate file called paper-color.css. But now I can't find that code anywhere, not in the book I was editing, not in stylesheet.css and I can't find the paper-color.css file.

I copied the book to my Kobo Vox, and it worked. It was really late so I didn't try any other books. But today I find everything I open on Kobo has the soft beige background color.

Its not really a problem, as that is the colour I want as a default on Kobo, but it is annoying that I can't find it! Plus I am totally confused why all the books that were already on my Kobo show this mod.