Log:

05.13 - 02.50am - Update
05.02 - 06.07am - Released

Update: I have detected a problem with the filter regarding some sites. Now there is an option to not use the filter, in case you are having this problem too. If brightness option is "without", brightness value can be ignored.

Features:
This style provides a different eye protection, it will produce a dull grey overlay in every page. However there is a known issue that I still working to overcome¹.

How to choose values:
Brightness: Is in decimals, define how dark the whole screen will be. Use small values, 1 is default luminosity. It may not work in every browser².
Opacity: Defines how strong the dull effect will be, the lower the value more dullest it is.
Background: is in rgb, the higher the value the lighter the grey will be.

Explanation:
Instead using a image as overlay, as there is no way to do such ,each site has a different warp div name (or none at all), this style will change the html background to grey, and then proceed to down the opacity of all its children. It also use brightness filter² to compliment the effect, in case you browser don't support it, you can simple readjust the values.

¹Known issues:
Sites that uses the background direct on html or embedded an image on it, will end with the pure grey background, crashing against the others elements. Eg: google.com

Compatibility:
Using with light values I suppose it is compatible with another nightmode styles.

¹See known issues
²Please refer to https://developer.mozilla.org/en-US/docs/Web/CSS/filter