I have a theme that extends luma using _theme.less. On product pages, another CSS file is included in addition to styles-m. The problem is that they both @import _theme.less which results in duplicate CSS rules.
This will mess up any background images because they are included using relative paths.
With styles-m.css the path to images is: "../images/image.svg"
but gallery.css is in another subfolder so the path would have to be: "../../images/image.svg"
I am probably missing something here.