Update SelectPanel.playground.stories.tsx to no longer use styled-components

[hectahertz]

As we move away from styled-components, we would like to remove references and usage of the library in our storybook stories.

This issue tracks updating packages/react/src/experimental/SelectPanel2/SelectPanel.playground.stories.tsx to no longer use styled-components.

Copilot instructions

A story uses styled-components either directly or through other components or props. Make sure to migrate the story appropriate in the following situations:

• If using styled directly in a story, migrate it to a custom components without styled
• If using Box or BoxWithFallback, migrate to a custom component
• If using the sx prop, migrate to a class name

The project uses CSS Modules. For styles specific to a story, make a CSS Module next to the story and import the classes for custom components or styles from there.

It's important that you make no changes to the source files of components. All changes must be in the storybook stories.

(use PR title: Update SelectPanel.playground.stories.tsx to no longer use styled-components)

No need to add comments to the css modules that refer to the old styled-components styles or explain classes.

Please use clsx to combine classes in className.

Add the label 'skip changeset' to the created PR to fix this issue.

Please make sure to format the files.