Sample of how to organise Swift global constants

AppConstants.swift

import UIKit

struct Constants {

    struct Design {

        struct Color {

            struct Primary {

                static let Blue = UIColor(red: 0, green: 122, blue: 255, alpha: 1)
                static let BlueDisabled = UIColor(red: 28, green: 155, blue: 248, alpha: 1)
                static let Purple = UIColor(red: 80, green: 48, blue: 246, alpha: 1)
                static let PurpleDisabled = UIColor(red: 98, green: 68, blue: 255, alpha: 1)

            }

            struct Secondary {

                static let NeonBlue = UIColor(red: 0, green: 255, blue: 255, alpha: 1)
                static let Pink = UIColor(red: 255, green: 72, blue: 210, alpha: 1)
                static let Turquise = UIColor(red: 25, green: 221, blue: 227, alpha: 1)
                static let RedPurple = UIColor(red: 236, green: 26, blue: 81, alpha: 1)

            }

            struct Grayscale {

                static let Light = UIColor(red: 242, green: 243, blue: 248, alpha: 1)
                static let Mid = UIColor(red: 162, green: 163, blue: 177, alpha: 1)
                static let Dark = UIColor(red: 50, green: 48, blue: 70, alpha: 1)
                static let Black = UIColor(red: 21, green: 23, blue: 33, alpha: 1)

            }

        }

        struct Image {

            static let IcoCategory = UIImage(named: "ico_category")
            static let IcoClose = UIImage(named: "ico_close")

        }

        struct Font {

            static let Body = UIFont.systemFont(ofSize: 15, weight: .regular)
            static let Bold = UIFont.systemFont(ofSize: 15, weight: .bold)
            static let Sub = UIFont.systemFont(ofSize: 13, weight: .regular)
            static let Mini = UIFont.systemFont(ofSize: 10, weight: .medium)
            static let HeadingOne = UIFont.systemFont(ofSize: 24, weight: .semibold)
            static let HeadingTwo = UIFont.systemFont(ofSize: 20, weight: .semibold)
            static let HeadingThree = UIFont.systemFont(ofSize: 17, weight: .semibold)

        }

    }

    struct Content {

        static let Email = "rinalds@inbox.lv"
        static let Login = "Login"

        static let dummyText = "Lorem ipsum"
        static let dummyTextMedium = "Lore ipsum dolor sit amet"

    }

    struct API {

        static let twitterApiUrl = "https://api.twitter.com/"

        static let DB_REF = Firestore.firestore()
        static let USERS_DB_REF = DB_Ref.collection(USERS_REF)
        static let AUTH_REF = Auth.auth()
        static let USERS_REF = "users"

    }

}