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