emit proper error message for superfluous colon

src/value/parse.rs

@@ -606,6 +606,7 @@ impl Value {
                     Ok(IntermediateValue::Op(Op::Div))
                 }
             }
+            ':' => Err("expected \";\".".into()),
             v if v.is_control() => Err("Expected expression.".into()),
             v => {
                 dbg!(v);

tests/error.rs

@@ -19,3 +19,7 @@ error!(
     return_as_style,
     "a {@return foo;}", "Error: This at-rule is not allowed here."
 );
+error!(
+    colon_inside_style,
+    "a {foo: bar: baz;}", "Error: expected \";\"."
+);