fix signup & login input width

[shujuuu]

Fixes #3158

Changes:

• Fix the input fields' width for mobile
• Did a small refactor to the password input fields so the eye icon placement is dynamic

Login	Signup

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

[raclim]

This overall looks good to me! Thanks so much for working on this @shujuuu!