If you read the readme and the source. You would find that much of it was from Tim O Donnell's Google buttons. As my process 3 months ago I gave them a new CSS base, repainted and attached thin bevels. As for the colors I matched the colors and gradients from Microsoft's websites. I barely touched bootstrap for the buttons except for the dropdown, the radio button javascript are hand-made. The form elements and icons however are a different story, they came from Bootstrap and Syncfusion.

All sources are transparently mentioned in the acknowledgements section of the readme.