[Bugfix:CourseMaterials] Overlapping Buttons in UI

[immortalcodes]

Please check if the PR fulfills these requirements:

• [ ] Tests for the changes have been added/updated (if possible)
• [ ] Documentation has been updated/added if relevant

What is the current behavior?

Fixes #8248 Currently, the buttons overlap each other.

What is the new behavior?

After the addition of the margin, they don't overlap.

[codecov[bot]]

Codecov Report

Merging #8274 (066d96c) into main (27b299a) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##               main    #8274   +/-   ##
=========================================
  Coverage     21.94%   21.94%           
  Complexity     7713     7713           
=========================================
  Files           208      208           
  Lines         25135    25135           
  Branches         66       66           
=========================================
  Hits           5515     5515           
  Misses        19556    19556           
  Partials         64       64           

Flag	Coverage Δ
autograder	20.28% <ø> (ø)
js	28.74% <ø> (ø)
migrator	99.20% <ø> (ø)
php	20.09% <ø> (ø)
python_submitty_utils	71.65% <ø> (ø)

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