docs: implement dark mode

[sreetamdas]

Picking up from #247, I've implemented changes for the following:

In dark mode:

• inline code
• inline code with links

In light mode:

• inline code with links

There was also a warning with the aria-hidden tag on the landing page that has been fixed.

Attaching a screenshot to highlight the changes for the dark mode below; I had tweak the shade of purple being used for the code a elements. There were infima-based vars available in the custom.css file, so I went ahead and used those.

Since accessibility was one of the reasons that previous attempts didn't go through, I tried to make sure that there was enough contrast with the shades chosen (purple isn't easy to implement dark mode with 😅). Here's the results:

Before:

Mode	Element	Contrast
Light	code a	4.43
Dark	code	5.26
Dark	code a	1.06

After:

Mode	Element	Variation	Contrast
Light	code a		5.15
Dark	code		8.38
Dark	code a	inherited color	2.77
Dark	code a	"light" purple	3.33
Dark	code a	"lighter" purple	4.87

Would love to see dark mode getting finally enabled for the docs, please feel free to make any tweaks/suggestions that you'd like.

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[markerikson]

Thanks!