fix: fixed hover color issue throughout MFE

[sundasnoreen12]

INF-1220

Description

1. Updated the direct color codes in scss file with paragon color variables in discussion MFE.
2. Fixed hover color issue throughout discussion MFE
3. Fixed ZIndex issue of card

How Has This Been Tested?

Screenshots/sandbox (optional):

Include a link to the sandbox for design changes or screenshot for before and after. Remove this section if it's not applicable.

|Before|After|
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After

Post-merge Checklist

• Deploy the changes to prod after verifying on stage or ask @openedx/edx-infinity to do it.
• 🎉 🙌 Celebrate! Thanks for your contribution.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (92adec3) 92.38% compared to head (e9efc83) 92.38%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #644   +/-   ##
=======================================
  Coverage   92.38%   92.38%           
=======================================
  Files         169      169           
  Lines        3452     3452           
  Branches      892      892           
=======================================
  Hits         3189     3189           
  Misses        243      243           
  Partials       20       20           

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[awais-ansari]

LGTM. Just a nit. Add border around add comment button.