Detect dank mode on Mac OS

src/slic3r/Utils/MacDarkMode.mm

@@ -0,0 +1,22 @@
+#import "MacDarkMode.hpp"
+
+#import <Foundation/Foundation.h>
+
+
+@implementation MacDarkMode
+
+namespace Slic3r {
+namespace GUI {
+
+bool mac_dark_mode()
+{
+    NSString *style = [[NSUserDefaults standardUserDefaults] stringForKey:@"AppleInterfaceStyle"];
+    return style && [style isEqualToString:@"Dark"];
+
+}
+
+
+}
+}
+
+@end