The below links and images take you to the website which shows the designs of the Apple IOS, it shows how everything should be laid out, what colours to use, the hierarchy etc.
https://material.io/collections/get-started/#ios
https://developer.apple.com/design/human-interface-guidelines/ios/overview/themes/
The below links and images are from the Android design theme, it shows how everything should be displayed and laid out, the colours they used, the necessary hierarchy etc.
JWL 2020 