Answer 1

make a fake border with two overlayed linear-gradients . Then you can do border-radius.

Answer 2

See here:
https://stackoverflow.com/questions/51496204/border-gradient-with-border-radius#51496341

Answer 3

Lisa
great reference. Bookmarked.😎

Answer 4

#d1 {
height:649px;
border: double 1px transparent;
border-image-slice: 1;
border-width: 10px;
background-image: linear-gradient(white,white),linear-gradient(to left, #67FCC1FF , #84F1E0FF , #66E6D2FF , #5EE8FFFF , #28ACFFFF);
border-radius:26px;
background-origin:border-box;
background-clip: content-box, border-box;
}

Answer 5

border-image does not support border-radius.
The workaround is to fake the effect.