Fixed typo in basic css lesson

[rmhassan]

The lesson states: "You can think of the :root element as a container for your entire HTML document, in the same way that an html element is a container for the body element."

This should be CSS instead of HTML. It should read: "You can think of the :root element as a container for your entire CSS document, in the same way that an html element is a container for the body element."

This issue is opened in main repo, I have fixed the typo now.

Description

Pre-Submission Checklist

• [ ] Your pull request targets the dev branch.
• [ ] Branch starts with either fix/, feature/, or translate/ (e.g. fix/challenge-tests)
• [ ] All new and existing tests pass the command npm test.
• [ ] Use npm run commit to generate a conventional commit message. Learn more here: https://conventionalcommits.org/#why-use-conventional-commits
• [ ] The changes were done locally on your machine and NOT GitHub web interface. If they were done on the web interface you have ensured that you are creating conventional commit messages.

Checklist:

• [ ] Tested changes locally.
• [ ] Addressed currently open issue (replace XXXXX with an issue no in next line)

Closes #XXXXX

[scissorsneedfoodtoo]

@Hassanraja447, thank you for taking the time to submit a PR for this issue. Unfortunately, a fix was just merged with https://github.com/freeCodeCamp/curriculum/pull/315. Please check out our other open issues, and we're looking forward to your next contribution!