Change the style for all the courses button at course_selection page to look better

[sidharthkmishra]

Manual Test:

1. Open https://www-student.cse.buffalo.edu/CSE442-542/2019-Summer/cse-442a/
2. Enter mail id - smishra9@buffalo.edu
3. Click on Get Code button
4. Check if smishra9@buffalo.edu receive the confirmation code
5. Go to https://www-student.cse.buffalo.edu/CSE442-542/2019-Summer/cse-442a/index.html#tabs-2
6. Enter the confirmation code received at step 4 and the Email ID smishra9@buffalo.edu
7. Click on the Login button
8. Now all the courses for smishra9@buffalo.edu would have been shown at UI. Check the styel for each button