Enhance UI and Responsiveness

[Aman-Jangid]

Changes :

• Moved course and testimonial data into separate modules.
• Created separate folders for styles and data.
• Made the page responsive on most screen sizes.
• Fixed course card size on large screens.
• Made changes to some UI elements like signin,login buttons.
• Increase spacing between sections.
• Fixed Image scaling in course cards.
• Fixed all navbar links moving when a single one is hovered.

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