Fix Send Invitation Modal on Mobile and Narrow Screen

[suhyun-yun]

[FrontEnd] Fix Send Invitation Modal on Mobile and Narrow Screen

Description

When the screen is narrow, the modal breaks. Modal is also somehow "scrollable" on mobile.

Acceptance Criteria

• Input field and text-overflow (including email and schedule's name) are adjusted automatically to fit the screen ratio.
• Modal should be fixed (i.e., nothing aside from the list of emails is able to move).