use gradient as a border css code example

Example 1: css gradient border

box-sizing: content-box;
  border-width: 8px;
  border-style: solid;
  border-image: linear-gradient(to right bottom, #260B3C, #a053df);
  border-image-slice: 1;

Example 2: css border top linear gradient

.bordertest {
    height:300px;
    width:300px;
    border-top:30px solid #c4268c;
    background:#000;
    position:relative;
    margin:1em;
}
.bordertest:first-child:before {
    content:'';
    position:absolute;
    width:100%;
    height:30px;
    background:linear-gradient(to left, #c4268c, #9a0b72);
    top:-30px;
    left:0;
}