Styling Contact Form 7 in Block Theme (Twenty Twenty-Three)

I am stuck styling the contact form in the block theme Twenty Twenty-Three. I am using custom css and it works in a classic theme.

I am aware of this tutorial https://fullsiteediting.com/lessons/custom-block-styles/ and according to below quotation I need “prefix” and “slug” to give it a start.

“You are not limited to styling blocks from WordPress core. If you know the prefix and the slug, you can also style blocks from plugins.”

Can you provide with both, or a full example if you have, or point me into the right direction, if am wrong.

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