The truth is that very cool to have a gradient border, at first I thought it was impossible but the fact is that there is a function in css called border-image. You create a transparent border first and give it the border-image option as follows:
border: 10px solid transparent; //You create the edge border-image: linear-gradient(to bottom, #3acfd5 0%, #3a4ed5 100%) 1; //add the gradient to the corners
And it is already that simple. Any questions you have, comment and I will gladly help you.