Added an experimental light theme and automatic system theme detection

modules/theme.py

@@ -0,0 +1,52 @@
+# "modules/theme.py", licensed under the MIT license
+# Copyright 2024-2025 NinjaCheetah & Contributors
+
+import platform
+import subprocess
+
+def is_dark_theme_windows():
+    # This has to be here so that Python doesn't try to import it on non-Windows.
+    import winreg
+    try:
+        registry = winreg.ConnectRegistry(None, winreg.HKEY_CURRENT_USER)
+        key = winreg.OpenKey(registry, r"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize")
+        # This value is "AppsUseLightTheme" so a "1" is light and a "0" is dark. Side note: I hate the Windows registry.
+        value, _ = winreg.QueryValueEx(key, "AppsUseLightTheme")
+        return value == 0
+    except Exception:
+        return False
+
+def is_dark_theme_macos():
+    # macOS is weird. If the dark theme is on, then `defaults read -g AppleInterfaceStyle` returns "Dark". If the light
+    # theme is on, then trying to read this key fails and returns an error instead.
+    try:
+        result = subprocess.run(
+            ["defaults", "read", "-g", "AppleInterfaceStyle"],
+            capture_output=True, text=True
+        )
+        return "Dark" in result.stdout
+    except Exception:
+        return False
+
+def is_dark_theme_linux():
+    try:
+        import subprocess
+        result = subprocess.run(
+            ["gsettings", "get", "org.gnome.desktop.interface", "gtk-theme"],
+            capture_output=True, text=True
+        )
+        # Looking for *not* "Light", because I want any theme that isn't light to be dark. An example of this is my own
+        # KDE Plasma setup on my desktop, where I use the "Breeze" GTK theme and want dark NUSGet to be used in that
+        # case.
+        return not "light" in result.stdout.lower()
+    except Exception:
+        return False
+
+def is_dark_theme():
+    system = platform.system()
+    if system == "Windows":
+        return is_dark_theme_windows()
+    elif system == "Darwin":
+        return is_dark_theme_macos()
+    else:
+        return is_dark_theme_linux()