feat(embed): Add support for dark mode

[kakkokari-gtyih]

What

• Added support for dark mode by using tailwindcss dark: modifier.
  • Dark mode is also supported on the landing page.

Why

Fix #5119
Fix #5966
Close #6842 (I should have said in either of the 2 issues above that I'm working on the patch, sorry for duplication)

Additional Info

[gaearon]

Hi! Are there any design differences with #6842? I'm not completely opposed to explicit customization but I'd suggest separating that out — I'm not sure we want that. I'd like to better understand the design tweaks first though.

[kakkokari-gtyih]

I'm not completely opposed to explicit customization but I'd suggest separating that out — I'm not sure we want that. I'd like to better understand the design tweaks first though.

Okay, I'll separate the customization part (will create another issue once this or #6842 got merged).

Are there any design differences with #6842?

There might be slight color difference compared to that, but not so much as that in terms of design.
This implementation uses tailwindcss's dark: modifier, which is a recommended way to implement dark mode

[kakkokari-gtyih]

Okay, I'll separate the customization part.

done!