(* ::Package:: *)
values = "
opacity: 0.9
opacity: 90%
/* Global values */
opacity: inherit;
opacity: initial;
opacity: revert;
opacity: unset;
";
all = Sort@StringCases[
values,
RegularExpression[":\\s*([a-zA-Z0-9-]+);"] :> "$1"
];
"[\"" <> StringRiffle[all, "\",\""] <> "\"].contains(&mode)"