Currently, the Gmail Dark Theme, when you open an email, the background is white, and that is not what you would expect in a "dark" theme. My style changes de background to a dark grey and adjusts the color of the texts for better visibility. I'm using the default Dark Theme as a template, so it has to be active for this styles to work. Also, this is a work in progress, so some areas are still with a white background, like the reply and the chat window. This will be changed in time, but for the time being, the style is usable.