background-image: linear-gradient(direction, color-stop1, color-stop2, ...);
Direction - Top to Bottom (this is default)
background-image: linear-gradient(to right, red , yellow);
background-image: linear-gradient(to bottom right, red, yellow);
background-image: linear-gradient(angle, color-stop1, color-stop2);
background-image: linear-gradient(180deg, red, yellow);