Function load_stylesheet 

pub fn load_stylesheet(theme: &ThemeConfig) -> Stylesheet

Load the stylesheet selected by [theme].

In the default custom mode this prefers $XDG_CONFIG_HOME/tree-space/main.css, writing the shipped default out on first launch (see [ensure_default_stylesheet]) so there is always a file to edit. In system mode the file is ignored entirely — neither read nor created — and the theme comes from the configured desktop provider.