Phew, GitHub is over seven years old now... and is unquestionably synonomous with open source. After 7 years, those GitHub ribbons are more than overdue for a cleaner, more modern alternative. This is my take.
By using SVG, these corners can be clean and sharp. Any color, and size. As well as have a little character... on hover for desktop, and on page load for mobile devices.
You can build your own with the SVG's, copy some of the pre-defined code below, or just change the
color values on the main