What minimal example or steps are needed to reproduce the bug?

select {
	appearance: base-select;
}

What minimal configuration is needed to reproduce the bug?

{
    "rules": {
        "declaration-property-value-no-unknown": true
    }
}

How did you run Stylelint?

Demo

Which Stylelint-related dependencies are you using?

{
	"stylelint": "16.24.0"
}

What did you expect to happen?

No problems to be reported.

What actually happened?

The following problems were reported:

example.css
2:14-25 error Unexpected unknown value "base-select" for property "appearance" (declaration-property-value-no-unknown)

Do you have a proposal to fix the bug?

Update syntax in CSSTree.

For temporary use, you can extend the syntax yourself:

{
	"languageOptions": {
		"syntax": {
			"properties": { 
				"appearance": "| base-select",
			}
		}
	}
}