Make header sticky and other minor changes

[nabroleonx]

This PR fixes [#839]

These are minor changes but crucial for user experience, the website's header moves up when scrolling, and users have to scroll back up to use the navigation, which isn't ideal. So I have made the header stick to the top. I also made changes to volunteer.md, the links for the tech stacks weren't working so I fixed them.

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[nabroleonx]

@LayaTaal Ok, let me fix that real quick. By the way are these pull request hacktoberfest acceptable?

[nabroleonx]

@LayaTaal Check it now, it is fixed. I accidentally pushed yarn.lock by mistake but I have committed a corrective commit so it should be fine. If there is anything else you come across, Let me know.

[LayaTaal]

@LayaTaal Ok, let me fix that real quick. By the way are these pull request hacktoberfest acceptable?

Yep, you should get credit toward Hacktoberfest for anything merged here!

[nabroleonx]

@LayaTaal I did what you asked. Hopefully, I did it the way you want to but if there is anything I missed, let me know and I would be happy to correct it. Can you also label hacktoberfest to this issue so my PR can count for hacktoberfest :)

[nabroleonx]

Can you merge the pull request if

[nabroleonx]

@LayaTaal Can you merge the PR if it satisfied your request.