fix: missing elevated card shadow on dark mode

[tiffanynwyeung]

Description of changes

This change fixes missing box shadows on the elevated variation of the Card component. This is because dark mode shadow colors are not defined so it defaults to the light mode shadows, which are extremely difficult to spot in dark mode.

This change also visually changes/affects the dark mode versions of other components that use box shadows in general: Authenticator, Menu, and Slider Field.

• adds dark box shadow colors to dark mode override

Before	After
Card	Card
Authenticator	Authenticator
Menu	Menu
Slider Field (thumb)	Slider Field (thumb)

Issue #, if available

Fixes #5893.

Description of how you validated changes

Checklist

• [x] Have read the Pull Request Guidelines
• [x] PR description included
• [x] yarn test passes and tests are updated/added
• [x] PR title and commit messages follow conventional commit syntax
• [x] If this change should result in a version bump, changeset added (This can be done after creating the PR.) This does not apply to changes made to docs, e2e, examples, or other private packages.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: fe9458f94576678a3b9bf31bfb63d5e11a53db8a

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 14 packages

| Name | Type | | ---------------------------------------- | ----- | | @aws-amplify/ui | Patch | | @aws-amplify/ui-react-auth | Patch | | @aws-amplify/ui-react-core-auth | Patch | | @aws-amplify/ui-react-core-notifications | Patch | | @aws-amplify/ui-react-core | Patch | | @aws-amplify/ui-react-liveness | Patch | | @aws-amplify/ui-react-native-auth | Patch | | @aws-amplify/ui-react-native | Patch | | @aws-amplify/ui-react-notifications | Patch | | @aws-amplify/ui-react-storage | Patch | | @aws-amplify/ui-react | Patch | | @aws-amplify/ui-vue | Patch | | @aws-amplify/ui-angular | Patch | | @aws-amplify/ui-react-geo | Patch |

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