<!DOCTYPE html> <html lang="en-US"> <head> <title>test of border-image-source: linear-gradient</title> <style> div.border { border: 30px solid black; border-image: linear-gradient(to bottom right, red, blue); width: 180px; height: 180px; } </style> </head> <body> <div class="border"></div> </body> </html>