[style]: Improve Newsletter Input Field for Better Usability

[akshay0611]

What's the style idea?

We need to improve the usability of the newsletter input field in the "Subscribe Our Newsletter" section on the sitemap.html page. Previously, the input field had a fixed width that didn't allow users to input long email addresses properly. The style was updated to make it consistent with the other pages and ensure users can enter longer email addresses without issues.

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After the change:

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