feat: env var to set custom css location

Set `IRONBAR_CSS` to load CSS from that path instead of regular path.

src/main.rs

@@ -21,6 +21,7 @@ use gtk::gdk::Display;
 use gtk::prelude::*;
 use gtk::Application;
 use std::future::Future;
+use std::path::PathBuf;
 use std::process::exit;
 use std::{env, panic};
 use tokio::runtime::Handle;
@@ -95,14 +96,19 @@ async fn main() -> Result<()> {
 
         debug!("Created bars");
 
-        let style_path = config_dir().map_or_else(
+        let style_path = env::var("IRONBAR_CSS")
+            .ok()
+            .map(PathBuf::from)
+            .unwrap_or_else(|| {
+                config_dir().map_or_else(
                     || {
                         let report = Report::msg("Failed to locate user config dir");
                         error!("{:?}", report);
                         exit(ErrorCode::CreateBars as i32);
                     },
                     |dir| dir.join("ironbar").join("style.css"),
-        );
+                )
+            });
 
         if style_path.exists() {
             load_css(style_path);