Вы можете попробовать это
background-image: -webkit-linear-gradient(left bottom, #ccc 0%, #ccc 25%, #bbb 25%, #bbb 50%, #ccc 50%, #ccc 75%, #bbb 75%);
background-image: -moz-linear-gradient(left bottom, #ccc 0%, #ccc 25%, #bbb 25%, #bbb 50%, #ccc 50%, #ccc 75%, #bbb 75%);
background-image: -ms-linear-gradient(left bottom, #ccc 0%, #ccc 25%, #bbb 25%, #bbb 50%, #ccc 50%, #ccc 75%, #bbb 75%);
background-image: linear-gradient(left bottom, #ccc 0%, #ccc 25%, #bbb 25%, #bbb 50%, #ccc 50%, #ccc 75%, #bbb 75%);