Slots for styling

[stephenwf]

At the top level, we could have slots that map components if you want to provide custom ones.

function MyCustomThumbnailWrapper({ children }) {
  //...
  return <div className="my-classname">{children}</div>
}

<ThumbnailPanel 
  slots={{
    thumbnailWrapper: MyCustomThumbnailWrapper,
    // ..
  }}
/>

[stephenwf]

Some examples of styling patterns here:

• https://mui.com/base/getting-started/customization/
• https://react-spectrum.adobe.com/react-aria/react-aria-components.html