iOS Human Interface Guidelines

iOS Human Interface Guidelines: 

• UI Design Basic. https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/index.html#//apple_ref/doc/uid/TP40006556-CH66-SW1
• Design Strategies
  https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/Principles.html#//apple_ref/doc/uid/TP40006556-CH4-SW1
• UI Elements
  https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/Bars.html#//apple_ref/doc/uid/TP40006556-CH12-SW1
• Icon and Image Design
  https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/IconMatrix.html#//apple_ref/doc/uid/TP40006556-CH27-SW1

The System Font, SF, for OS X, iOS, watchOS, and tvOS.

https://developer.apple.com/fonts/