Somewhere along the way, "dark mode" became a checkbox on a roadmap. It should be a habit — like holding the door.
It's about respect, not aesthetics
Someone opens your site at midnight and gets a faceful of white light. Someone else set a system preference for a reason you'll never know — migraines, eyesight, a sleeping baby. Honoring it costs you nothing and tells them everything.
The cost is smaller than the gesture
Done right — with design tokens instead of one-off colors — theming is nearly free to maintain and quietly says: we thought about you.
The details users never mention are the ones they feel.
This very site follows your system theme without asking. You probably didn't notice.
That's the point.