Simple Gray Default Button Clip Art at Clker.com - vector clip art online, royalty free & public domain
Focus indicator should be clearly visible while navigating to Primary Button, Default Button and close button in Dialog control · Issue #3714 · microsoft/fluentui · GitHub
A guide to BUTTON DESIGN & implementation | MiC
Styling The Good Ol' Button Element
How to indicate a default button in Material Design - User Experience Stack Exchange