Can I use design elements and functionality of someone else's site in my portfolio?

Question

Design

I want to get my hand in writing the code for the server and client parts of the site. And develop an elementary portfolio.
In order not to be distracted by inventing business logic/design/concept from scratch, I plan to find interesting sites on the Internet and somehow rewrite them with my own code while preserving the original design and functional elements.
Worried about whether I can then use these developments in my portfolio and post them on GitHub? Of course, stipulating that my authorship is only the code of the site, and not the design.

Answer 1

rewrite them with your own code while preserving the original design and functional elements.

Change colors, text and pictures - here's a new design for you, if you're not capable of your own. Absolutely tyrit someone else's so clearly - to your own detriment. At least some work on the content should be.

Answer 2

Not worth it. Demo materials in bulk.