Selected intern's day-to-day responsibilities include:

1. Determining the structure and design of web pages
2. Ensuring user experience determining design choices
3. Developing features to enhance the user experience
4. Striking a balance between functional and aesthetic design
5. Ensuring web design is optimized for smartphones
6. Building reusable code for future use
7. Optimizing web pages for maximum speed and scalability
8. Utilizing a variety of markup languages to write web pages
9. Maintaining brand consistency throughout the design
10. Developing and implementing highly responsive user interface components using React concepts

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