如何用CSS创建多色边框？

.container {
  position: relative;
  border: 5px solid transparent;
}

.container::before {
  content: '';
  position: absolute;
  top: -10px;
  left: -10px;
  right: -10px;
  bottom: -10px;
  z-index: -1;
  border: 5px solid red;
}

.container::after {
  content: '';
  position: absolute;
  top: -5px;
  left: -5px;
  right: -5px;
  bottom: -5px;
  z-index: -1;
  border: 5px solid blue;
}

.container {
  border: 5px solid;
  border-image: linear-gradient(to right, red, blue) 1;
}

.container {
  border: 5px solid;
  outline: 5px solid blue;
  box-shadow: 0 0 0 5px red;
}