Feat: Add Header Component Styling

[Adi-bit93]

Added comprehensive CSS styling for the Header component to improve the overall UI/UX of the navigation bar.

#Changes Made

1. Created CSS styles for .site-header and related elements
2. Implemented modern, clean design with professional color scheme
3. Added fully responsive layout for mobile and tablet devices
4. Added hover effects and smooth transitions on navigation links
5. Made header sticky with subtle shadow for better navigation experience

#Key Features

1. Sticky Header: Header remains fixed at the top while scrolling for easy navigation access
2. Hover Animations: Smooth underline animation on nav links for better user feedback
3. Responsive Design:
4. Desktop: Logo (left), centered navigation, cart (right)
5. Mobile: Logo and cart on top row, navigation links below
6. Visual Polish: Subtle box shadow and smooth transitions throughout
7. Accessibility: Good color contrast and readable font sizes

#Screenshots

Type: Enhancement
Priority: Medium

[Adi-bit93]

Hey, @Nikhil-2002 check the new Enhancement in Header