The same code will be rendered on the web hosting differently from my browser rendering the code off my computer

Does anyone have any idea on why the same code will be rendered on a web hosting differently from my browser rendering the code off my computer?

The code works perfectly if I run it on my browser from my computer, but it gets weird when I put it on my web hosting and run it on the internet. It even runs differently on different browsers! P.S.: It's definitely not an issue with files missing. I actually realized some of my css won't run on the web hosting, which is super weird. Why would that be? Let me know if you need to see any particular part of my code?

Thanks in advance!