How do I make the header fit entirely on the top? Please help me with this code

Question

Hello, as I said in the question, why isn't the header in this code fitting perfectly along the top and the sides. Will it be the same across all devices? And besides, the menu icon (three lines) is not showing up (it showed up in my PC).
Any help is appreciated. Thanks in advance 😉
https://code.sololearn.com/WQ383vPhQOMw/?ref=app

Answer 1

Mirielle, thanks a lot.
But why is the menu icon not showing. It worked on my PC

Answer 2

Should I insert it inside an <a> tag and then style it?