Code to reproduce:
Predicate<CssMetaData> predicate = (data) -> "-fx-alignment".equals(data.getProperty());
Button.getClassCssMetaData().stream().filter(predicate).forEach((e) -> System.out.println(e));

output :
CSSProperty {property: -fx-alignment, converter: EnumConveter[javafx.geometry.Pos], initalValue: CENTER_LEFT, inherits: false, subProperties: []}

in cssref.html default value "-fx-alignment" equals top-left