Adding simple hyperlink with popup.. CSS problem

Dear all,

I have a simple problem that I don't know how to solve. I have added a hyperlink in /public_html/gallery/themes/PGtheme/templates/mytemplate.tpl and this hyperlink should create a popup window. The template is mytemplate and it is reading theme.css correctly. But the popup html window resulted from the hyperlink don't read the css.

I have tried to add a style tag in the popup html window and it is also wasn't read.
Note: I have placed the popup window in /public_html/gallery/.

Could you please help me to make the popup window read the theme.css ?

Thanks