Fix css compilation in Windows

[yuuuxt]

In Windows the string self.to_sass() generates is like @import "some\path\in\windows...", which causes CompileError: Error: File to import not found or unreadable: somepathinwindows..., an escape character issue.

I assume a simple string replace can fix it.

[gadenbuie]

Thanks @yuuuxt. What's interesting to me is that we do exercise CSS compilation in our unit tests on Windows, so I have a suspicion there's more to this issue. Can you share more context including information about your operating system and a small app that reproduces the issue?

[yuuuxt]

@gadenbuie here is a quick demo using poetry and pyenv: https://github.com/yuuuxt/shiny_css_compilation_demo

Hope it's self-explained, and feel free to ask if it's not clear enough!

My OS is Win 10 22H2.

[gadenbuie]

Thanks for the reproducible example @yuuuxt! I've proposed a fix in #1684 that goes in a slightly different direction and directly fixes the file path strings.