Fix: Remove flex from .anchor-link

[MaoShizhong]

Because

.anchor-link's flex property was causing rendering issues with <em> children as per TheOdinProject/curriculum#27831.
Only just discovered as #4507 let level 4 headings generate > .anchor-link and that sole heading was the only occurrence of having a child tag splitting up the text content.

Flex is no longer needed for .anchor-link (those headings are the only things that currently use the class).

This PR

• Removes flex-related properties from .anchor-link
• Positions .anchor-link:hover::before due to lack of flexbox

Issue

N/A

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project Contributing Guide
• The title of this PR follows the keyword: brief description of change format, using one of the following keywords:
  • Feature - adds new or amends existing user-facing behavior
  • Chore - changes that have no user-facing value, refactors, dependency bumps, etc
  • Fix - bug fixes
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• I have verified all tests and linters pass after making these changes.
• If this PR addresses an open issue, it is linked in the Issue section
• If applicable, this PR includes new or updated automated tests

[KevinMulhern]

Looks great to me, thanks @MaoShizhong