Ensure custom CSS would not impact non-drupito USWDS components on the same page

Problem/Motivation

In rare cases, we need to add minimal custom CSS to a USWDS component to 'normalize' something (e.g. a paragraph passed into an alert component should not add its own padding because the USWDS alert already takes care of that.

And it's possible for this module to be combined with another USWDS implementation/theme, especially during a transition between the two.

We don't want any of our custom CSS to impact anything except our component, and we don't want to change the OOTB USWDS class names.

Proposed resolution

Use the SDC component-specific selector.

MR will be submitted shortly.