`:global` block produces invalid css for `SelectorList`

[paoloricciuti]

Describe the bug

Given a component like this

<style>
	:global {
		a, b {
			color: red;
		}
	}
</style>

the generated css looks like this

	/* :global {*/
		/* (unused) a, b*/ {
			color: red;
		}
	/*}*/

which is wrong because there's a block without a selector.

Reproduction

REPL

Logs

-

System Info

-

Severity

annoyance

[paoloricciuti]

This is probably a regression from #15762 since now here

svelte/packages/svelte/src/compiler/phases/3-transform/css/index.js

Lines 201 to 202 in bfb969a

	(!is_in_global_block(path) || node.children.length > 1) &&
	!path.find((n) => n.type === 'ComplexSelector' && !n.metadata.used)

even if we are in a global block we still modify the code because node.children.length is greater than 1