Replace grey border with a "tint + highlight".
Before
After
This is more in line with the material design spec:
https://www.google.com/design/spec/style/icons.html#icons-product-icons
(Look for "Edge tint and shade" in that document).
While this change doesn't adhere to the specific sizings or colours specified in that document (mainly because setting a "shade" on a 100% black background doesn't work), it is still faithful to the idea of a tint + shade.
The steps to reproduce this style were to:
- Remove the stroke from the background
- Duplicate the background, move it down 4px, then select the clone and the original background and take the difference of both. This creates the tint.
- Repeat for the shade, but move the duplicate up 4px before taking the diff.