IDE(s) vs Sololearn's Code Playground

Question

Why is the output of the exact same code of HTML, external CSS & external JS different?
https://sololearn.com/compiler-playground/WW6Q2Q9rJ2f2/?ref=app

Answer 1

you mixed up css, html and Javascript in the css tab, resulting in invalid code

Answer 2

randomly copy pasting things is not how web pages are made...