Improve main header button design

[marvin-j97]

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• This PR references an issue (except for typos, broken links, or other minor problems)

Description(required)

Replaces the bottom border with a glassy background color, which looks better and has better on hover feedback.

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[amirhhashemi]

I personally like this. However, we generally do not accept pull requests that alter the website's design. Design is highly subjective, and allowing design PRs could quickly lead to inconsistencies in our overall look and feel. While your design may appear better, it still doesn't align well with the design of the other buttons on the website.

I understand that our design isn't the most consistent, and I've voiced my own criticisms in the past. Nevertheless, for the reasons mentioned, I prefer to close this PR. Please feel free to share your feedback on Discord. In the next redesign of the website, or whenever a team member has some free time, we will try to address these concerns.

I also want to express my appreciation for the effort you put into this project. Thank you.