UX: Consider styling form inputs as boxes

[michaelbromley]

The Clarity design system which is used as the component library of the admin-ui styles form inputs as lines rather than boxes, in a similar way to the Material Design spec:

While this can look quite sleek and minimal, my personal feeling is that it can make it more difficult for the user to discern between an input and other page elements (such as separating lines between sections).

A case in point is this part of the ProductListComponent, where the input appears just above another couple of lines:

TODO: Research

Look for any existing UX research on this topic and take it from there.

[michaelbromley]

Note: It appears that even Google in their latest Material Design spec have moved away from the "underline" style for form inputs: https://material.io/design/components/text-fields.html#filled-text-field