fix(checkbox): update checkbox styles (#3793)
fix(checkbox): update checkbox styles (#3793)

Fixes #3691
shane-tomlinson/fxa-content-server,mozilla/fxa-content-server,shane-tomlinson/fxa-content-server,shane-tomlinson/fxa-content-server,vladikoff/fxa-content-server,mozilla/fxa-content-server,mozilla/fxa-content-server,vladikoff/fxa-content-server,vladikoff/fxa-content-server