border에 그라디언트 넣기

      border-top: 3px solid transparent;
      border-image: linear-gradient(90deg, rgba(253,29,29,1) 0%, rgba(252,176,69,1) 30%, rgba(142,255,121,1) 64%, rgba(131,58,180,1) 100%) 1;
      background-origin: border-box;
      background-clip: content-box, border-box;
      background: #fff;

    border-image의 맨끝 1은 꼭 넣기

     

    둥글기가 들어가있으면 적용되지 않음