Let’s be honest: If you are using Flash CS6 primarily for (coding games or apps), you should stop trying to force a dark mode into the IDE. Instead, use a modern code editor.
Tools like "Magnifier" (Windows) or "Accessibility" settings (macOS) allow you to invert screen colors. While this makes the UI dark, it also inverts your artwork's colors, which is usually counterproductive for design work. External Apps: adobe flash cs6 dark mode
So, the burning question is: