Dark theme for deno docs | Theming for deno docs

[nirnay-raval-st10]

• The Deno documentation is currently only available in a light theme. Many users prefer a dark theme for reading documentation, especially in low-light environments or at night. A dark theme would reduce eye strain and improve readability for these users. Additionally, a dark theme can make the documentation more visually appealing and modern.

[nirnay-raval-st10]

copy of #817