Improve dark mode color pallete

[0xpili]

In dark mode, the background color is currently green, which I believe doesn't align with GraphOps branding colors.

ChatGPT suggested to use the following colors for dark mode:

• Background color: Dark gray or near black (e.g., #121212, #1E1E1E, or #000000) to reduce eye strain and contrast harshness.
• Primary text color: Light gray or white (e.g., #FFFFFF, #E0E0E0) for clear readability against the dark background.
• Secondary text color: A softer gray (e.g., #B0B0B0) for less prominent text like subtitles or meta information.