Here in Canada it's dark the first couple hours when I'm up on a winter morning, then dark again starting early eve. So dark mode help reduce my eye strain a lot.
To turn dark mode on / off, click the toggle in the top right of the screen:
I love the dark mode feature - but one thing that would make it even nicer would be to have two colors associated with each Category (one for light mode, one for dark mode), and switch as the mode is changed. As is, it can be hard to read the Category links in one of the modes.