[Cashtab] Patch input field border css

Summary: Correct an unintended change introduced in D17154 when converting Inputs.tsx to typescript

Test Plan:
npm test

current style in prod (unintended)

intended style

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17184