Show how to merge classes passed as props when children have existing classes

[aretrace]

📚 Subject area/topic

Component classes

📋 Suggested page

https://docs.astro.build/en/guides/styling/#passing-a-class-to-a-child-component

📋 General description or bullet points (if proposing new content)

Currently, the docs do not show what to do when you pass a class to a child component while the component already has its classes. How would you merge the class passed as a prop with the existing classes in a child component?

🖥️ Reproduction of code samples in StackBlitz

No response