Shadows can be too dark

If someone is using the shadow props and NOT building a dark theme while the user is in a prefers dark mode, the shadows adapt to the preference and are overly dark in the light document.

I think we'd need a media query for `color-scheme` in order to properly handle it. then the shadows could pivot on that instead of the media query.

Start by locating the shadow props and the media-query definitions that make them respond to dark-mode preferences. Reproduce the issue in a light document with prefers dark mode enabled, then verify that the shadows no longer become overly dark when no dark theme is being built.

Written by the indexing model from the issue text.