Funny that this website does not respect the user's OS settings at all.
in my made up, undersourced version of tech history, what happened was that the first LCDs that came out were very dim compared to the CRTs they were replacing, which OS makers responded to by going to very bright/white UIs over the previous gray/color schemes that were used and everyone cranked their brightness to 11. Over time LCDs improved and the new white-standard/high brightness regime became untenable for people who were on their screens for long periods of time, which drove the creation of dark mode, first in coding themes and later for the entire OS.
Dark mode support makes it VERY hard to do a website well because it is almost always going to look mediocre in one mode or the other and it is very easy for a gremlin to sneak in in the mode that a developer isn't using.
I would love to go back to a gray-base color and use a mildly muted white for a reading background and dark for code/special content. The hyperscript website is kind of a gesture in this direction: https://hyperscript.org/
It's funny noticing how most Electron/WebViews/web-sites immediately switch too, and have good dark mode support, while non-web-tech native apps either only support light-mode, have a bad looking incomplete dark-mode, or require a restart to switch.
So much for "native GUIs are superior, consistent and respect the user". Microsoft is still struggling with adding dark mode support to most Windows included apps.