Error when using multiple CSS selectors

Let me remind you about the rookie mistake: the selector .bbb.zzz and the selector .bbb .zzz do different things. The first one looks for an element that has two classes at the same time, and the second one looks for an element with the class zzz, located inside the class bbb.

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

h2.zzz {
	color: red;
}

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

h2 .zzz {
	color: red;
}

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

.bbb.zzz {
	color: red;
}

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

.bbb .zzz {
	color: red;
}

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

.bbb.zzz.xxx {
	color: red;
}

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

.bbb .zzz.xxx {
	color: red;
}

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

.bbb.zzz .xxx {
	color: red;
}

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

.bbb .zzz .xxx {
	color: red;
}

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

#elem.bbb {
	color: red;
}

Explain what the selector in the code below selects. Then write the HTML code that matches that selector. Here's the code with the selector:

#elem .bbb {
	color: red;
}