CSS渐变色圆角边框

.box {
  border: 3px solid transparent;
  border-radius: 100px;
  background-clip: padding-box, border-box;
  background-origin: padding-box, border-box;
  background-image: linear-gradient(to right, #fff, #fff),
  linear-gradient(to right, #8f41e9, #578aef);
}

效果图：