feat: use appearance to style radio buttons and checkboxes

[greatislander]

• I've read the guidelines for Contributing to the Platform Co-op Toolkit
• This isn't a duplicate of an existing pull request

Description

Uses appearance: none to remove default radio button and checkbox styles instead of relying on the label being adjacent to the element.

TODO:

• Support styling radio and checkbox labels differently from other form element labels.

Steps to test

1. Review checkbox, custom checkbox and radio button components.

Expected behavior: They match the current styling.

Additional information

Not applicable.

Related issues

• Resolves The CSS rules for form elements should be more flexible to accomodate different ways of structuring valid forms #286.
• Resolves Try improved method for styling radio buttons and checkboxes #342.

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[cherylhjli]

The radio buttons look like checkboxes now o_o

[greatislander]

@cherylhjli Oops! Try again once this deploy preview builds.