How to create a good side bar?

Question

Why my code is not working? Is there any unwanted styles in my code? Please say tips to improve my side bar ?
https://code.sololearn.com/Wkb2zLAHJ6sU/?ref=app

Answer 1

W3.CSS Sidebar

https://www.w3schools.com/w3css/w3css_sidebar.asp

Answer 2

Khasan and SoloProg thanks for your answers.
But I want to find what is the reason of failing side bar!