<linearGradient id="grad" x1="0" x2="0" y1="0" y2="1">y2 заменить значение с 1 на 100%:<linearGradient id="grad" x1="0" x2="0" y1="0" y2="100%">gradientUnits со значением userSpaceOnUse:<linearGradient id="grad" x1="0" x2="0" y1="0" y2="100%" gradientUnits="userSpaceOnUse">gradientUnits.