[web] update password change modal css to use camalcase

Summary:
As I was visually cleaning up the password change modal, I noted that the css was in snake case instead of camel case. To keep everything consistent with the rest of the code base, I updated the casing here to be camel case

Depends on D10241

Test Plan: flow and confirmed that the password change modal had no visual regressions

Reviewers: atul, rohan, kamil

Reviewed By: rohan

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10242