Added child combinators explanation

[rampichino]

Because

Fix the issue of the child combinator > used in the examples but still not covered in the section.

This PR

• Move the content of Not everything adds to specificity outside the note box and make it a subsection.
• Rephrase the first senteces below the new subsection.

Issue

Closes #30067

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide

[ManonLef]

@rampichino I have read in your issue that this was your first PR to a public repo. You did very well and @mao-sz left you a review comment/suggestion.

There are multiple ways to solve this:

1. you can make the changes manually on your computer on the same branch, then commit and push them, OR (even easier):
2. you can click the "commit suggestion" button on Mao's suggestion
   

Once that is done and all review comments are addressed (just one in this case) you can click on the "re-request review" icon in the top right corner next to the reviewers.

Feel free to let any of us know if you need any help or if something is unclear.

[rampichino]

@ManonLef I did the changes. Thanks for the suggestions.

[mao-sz]

Many thanks. There was a funky merge conflict due to a recent renaming of some files so I've sorted that out.