Dark mode theme is not flattering - colors in images should be inverted for a better appearance

[lizababu]

Most images have either a white/transparent background and black text. When in dark mode, these are not flattering, there is either a white square that hits you in the eye, or black text on a dark background which is difficult to read.

TODOs:

• Make all images with transparent background.
• Create a duplicate image for each existing image, but with inverted colors.