[UI/UX:InstructorUI] Fix rubric points input background color (#6480)
[UI/UX:InstructorUI] Fix rubric points input background color (#6480)


RCOS-Grading-Server/HWserver,Submitty/Submitty,RCOS-Grading-Server/HWserver,Submitty/Submitty,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,Submitty/Submitty,Submitty/Submitty,Submitty/Submitty,Submitty/Submitty,RCOS-Grading-Server/HWserver,Submitty/Submitty,Submitty/Submitty,Submitty/Submitty