Added --custom-system-css to specify a custom "system" CSS file

src/functions.vala

@@ -80,6 +80,9 @@ namespace SwayNotificationCenter {
             // Load packaged CSS as backup
             string system_css = get_style_path (null, true);
             system_css = File.new_for_path (system_css).get_path () ?? system_css;
+            if (custom_packaged_css != null) {
+                system_css = custom_packaged_css;
+            }
             if (!skip_packaged_css) {
                 message ("Loading CSS: \"%s\"", system_css);
                 system_css_provider.load_from_path (system_css);

src/main.vala

@@ -9,6 +9,7 @@ namespace SwayNotificationCenter {
     static string ? config_path;
     // Dev args
     static bool skip_packaged_css = false;
+    static string ? custom_packaged_css;
 
     public class Swaync : Gtk.Application {
 
@@ -84,6 +85,9 @@ namespace SwayNotificationCenter {
                         case "--skip-system-css":
                             skip_packaged_css = true;
                             break;
+                        case "--custom-system-css":
+                            custom_packaged_css = args[++i];
+                            break;
                         case "-c":
                         case "--config":
                             config_path = args[++i];
@@ -131,6 +135,8 @@ namespace SwayNotificationCenter {
             print ("\t -c, --config \t\t Use a custom config file\n");
             print ("\t --skip-system-css \t Skip trying to parse the packaged Stylesheet file."
                 + " Useful for CSS debugging\n");
+            print ("\t --custom-system-css \t Pick a custom CSS file to use as the \"system\" CSS."
+                + " Useful for CSS debugging\n");
         }
     }
 }