Gradient border color on a box

border.css

.border {
  position: relative;
  background-clip: padding-box;
  border: 1px solid transparent;
  border-radius: var(--brand-borderRadius-large);
}

.border::before {
    content: "";  
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    z-index: -1;
    margin: -1px;
    background: linear-gradient(#89898a, #37393d);
    border-radius: inherit;
}