To install it click here for instructions. You will need to have Tampermonkey installed to run it, but the installation instructions will tell you how to do that, if you don't know how to yourself.
Today I've found a perfect for me dark mode plugin made by sigma_g and greatly improved on by Lord_David. Sadly it was broken and unmaintained for over 2 years, so I've decided to fix it and improve it a bit. So a new dark theme plugin was born, which you can now use yourself.
The plugin also slightly tweaks the rating colors for them to look nicer on a dark background, you can see the table of changed colors here.
Also you might have noticed there are two versions of the theme: the white nutella and the black nutella. The word nutella here refers to the legendary grandmaster rating color scheme(the first letter is black and the rest are red). The white nutella version changes the first letter to be white, meanwhile the black nutella version leaves the first letter as is. Choose whichever one you like best!