background: linear-gradient(90deg, #3b82f6 0%, #8b5cf6 100%);

/* With fallback */
background: #3b82f6;
background: linear-gradient(90deg, #3b82f6 0%, #8b5cf6 100%);

/* As CSS variable */
:root {
  --gradient-main: linear-gradient(90deg, #3b82f6 0%, #8b5cf6 100%);
}

/* Usage */
.element {
  background: var(--gradient-main);
}

/* Border gradient trick */
.element {
  border: 2px solid transparent;
  background: linear-gradient(white, white) padding-box,
              linear-gradient(90deg, #3b82f6 0%, #8b5cf6 100%) border-box;
}