Dark and dark dimmed themes are now generally available to all github.com and GitHub Enterprise Cloud users. The updated appearance settings included in this release are designed to give you more control over your theme preferences. Select
Single theme or
Sync to system to customize the themes that are active during day and night. GitHub will now default to match system preferences when a user is logged out, or when a user is logged in and theme preferences have not yet been set. Manage your theme settings in the "Appearance" tab located in your profile settings.