Fix keyboard mask checkbox css

[Jack-Byrne]

Testing Plan

• I have verified that I have not introduced new warnings in this PR (or explain why below)
• I have tested this PR against Core and verified behavior (if applicable, if not applicable, explain why below).

Core Tests

• Set global properties with keyboard user input mask enabled
• Verify placement of checkbox

Core version / branch / commit hash / module tested against: 8.0
Proxy+Test App name / version / branch / commit hash / module tested against: rpcb-js

Summary

Fixes CSS of the user mask checkbox. It was previously wrapped and non-visible in the parent div.

CLA

• I have signed the CLA

[iCollin]

if you like the checkbox on the top of the text input, the PR is great as is.
on master, the checkbox is vcenter, so I have left suggestions to vcenter it here as well