text, SVG and GIF transparency

[s314cy]

currently, common browser extensions bringing dark themes to websites work particularly well on disco

yet, a few cosmetic changes remain to be done:

• white text/SVGs should instead be transparent (text-transparent tailwind class)
• all three GIFs (disco logo and decentralized/federated diagrams) should have a transparent background (no idea of how this works for GIFs)
  • right now, the background color is hardcoded to match the current background of the containing page
• the MLO png logo should have an alpha channel of 0 for its white background