Are there current standards or guidelines regarding dark themes / dark modes?

Many people are starting to realize that they prefer what is commonly called "Dark Mode" or "Dark Theme". That is, light text on a darker background.

As such, developers are now scrambling to create dark themes for their websites, applications, and operating systems.

The resultant set of themes represent a hodgepodge of different ideas of what a "dark theme" should look like. Some are pure white (#FFF) on pure black (#000), while others are variations within those two extremes.

I have been creating (and usability testing) dark themes for over two decades now, and consequently have my ideas and experiences on what works best. But are there now any recommended standards or guidelines for how dark to make the dark backgrounds, and how light to make the light text? What about the specific colors to use, as "dark" and "light" come in millions of different hues?

I found this question, but it only addresses contrast, which is not quite what I'm getting at. Contrast refers to relative intensity variability, whereas I am also inquiring about overall levels of brightness as well as color hues.