linear-gradient(0deg, #ffec3f 0%, #ffec3f 50%, #fbd424 50%,#ffe02d);
Is minified to:
linear-gradient(0, #ffec3f 0%, #ffec3f 50%, #fbd424 50%,#ffe02d);
(It changes 0deg, to just 0). This is then no longer valid as: "The angle the gradient line should assume, expressed as a number followed by an angle units designator(for instance, "deg")"
It subsequently does not work in IE10 (and likely other browsers, however their vendor specific prefixed versions still carry on working).