deg
0%
100%
Indigo
Sunset
Ocean
Forest
Fire
Aurora
background: linear-gradient(135deg, #6366f1 0%, #8b5cf6 100%);
Full rule:
.element {
  background: linear-gradient(135deg, #6366f1 0%, #8b5cf6 100%);
}
As background-image:
background-image: linear-gradient(135deg, #6366f1 0%, #8b5cf6 100%);