fix course mgmt overlay bug

[mono424]

Motivation and Context

If lectures are sorted ASC, the option menu is below the next lecture section.

Description

Setting z-index to 10.

Steps for Testing

1. Log in
2. Navigate to a Course management page
3. Set sort to asc
4. Check if the menu is overlaying the next lecture row

Screenshots

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Logins

| Kurs1 | Kurs2 | Kurs3 | Kurs4 | | ---------------------------------------- | ------------------------- | ------------------------- | ------------------------- | | public | public | loggedin | enrolled | | prof1 | prof1 | prof2 | prof1
prof2 | | student1
student2
student3 | student1
student2 | student2
student3 | student1
student2 |