How do you darken the screen on Qubes OS?

I’m using Qubes OS, but I want to make it darker as the screen gets brighter.Also, do have any kind of night mode that is kind to your eyes? If not, please tell me the recommended software.
Since the screen will go to sleep immediately, where do you start from that setting? I want to extend my grace more.

I am not exactly sure what you are asking. but to make things a bit darker, we do allow you to set themes.

Go to : the start menu > systemtools > settings manager > appearance, then choose for Xfce dusk.