Using @position-try produces a warning

[samausir]

Describe the bug

Using @position-try produces the following warning:

Unknown at rule @position-try (css unknownAtRules)

Reproduction

@position-try --back-up {
	inset-inline-start: anchor(left);
}

Expected behaviour

No warning should be emitted, specially since there are no warnings emitted for other properties introduced in the anchor positioning APIs (e.g. anchor-name, position-try-options, etc.)

System Info

• OS: MacOS
• IDE: VSCode

Which package is the issue about?

Svelte for VS Code extension

Additional Information, eg. Screenshots

No response