[#12653] Copy course modal: Mandatory fields not highlighted

[leojiangxd]

Fixes #12653

Tried to replicate solution in [#12617].

[github-actions[bot]]

Hi @leojiangxd, thank you for your interest in contributing to TEAMMATES! However, your PR does not appear to follow our contribution guidelines:

• Description must reference the issue number the PR is fixing, e.g. Fixes #<issue-number> (or Part of #<issue-number> if the PR does not address the issue fully)

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[weiquu]

Hi @leojiangxd, do fix the failing checks. You can click on 'Details' to see more information. In particular, it seems like the lint check (npm run lint) and the snapshot tests are failing.

[cedricongjh]

closing due to inactivity, do reopen the PR if you're continuing work on the issue