Update welcome page buttons styling from square to rounded

[shivamb11]

Fixes: #27468

Changed buttons styling and added hover effect on them for improved user experience.

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• Sign-off given on the changes (see CONTRIBUTING.md).

Before:

After:

[florianduros]

Thanks for you contribution.
The changes are design related, we will wait for the opinion of the design team on it.

[shivamb11]

Sure thing. Glad to have worked on it.

[Hinaichigo]

Rounded doesn't mean necessarily better user experience. Round buttons and elements can be aesthetically distracting.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[MidhunSureshR]

Closing this since it's not really enough that the buttons are rounded, they also need to match thematically with the rest of the application. The Design team will tackle this soon.