Intermediate HTML and CSS, advanced selectors: fix broken css-tricks.com links

[Strange-can]

Because

links to css-tricks.com under pseudo-classes and pseudo-elements were broken.

This PR

• changed the "selectors" part of the link to "pseudo-selectors"

• the ::before and ::after link also got the "a" part changed to "b"

Issue

Closes #28876

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

[MaoShizhong]

Thanks for fixing all these links.