Best practices for web page styling with CSS? [closed]

Question

I have a website to design. I have information on how the page should look and interact. The problem is I'm not good in front-end design, and have put many many hours to get the hang of the stuff. Currently I use the CSS from sample sites in github to style my site, which seems to be an un-ethical way.

Question: how do you style webpages?

• Are there some really good tools?
• I would be deeply appreciated if a detailed answer will be provided or link to wiki will work as well.