fix: group trending guides in a ul

[huyenltnguyen]

Checklist:

• [x] I have read freeCodeCamp's contribution guidelines.
• [x] My pull request has a descriptive title (not a vague title like Update index.md)

This PR:

• Groups items in the Trending Guides section in a ul (closes https://github.com/freeCodeCamp/freeCodeCamp/issues/52189)
• Updates and cleans up the CSS as the DOM structure is different now

Screenshots

| Device | Screenshot | | --- | --- | | Desktop | | | Tablet | | | Phone | |