A Powerful , Extensible CSS Parser written in pure Swift.

let width = css.int(selector: "#View", key: "width") // Int
let height = css.double(selector: "#View", key: "height") //Double
let color1 = css.color(selector: "#View", key: "color1") //UIColor
let font1  = css.font(selector: "#View", key: "font1") //UIFont
let font2 = css.font(selector: "#View", key: "font2", fontSize: 14) //UIFont
let size = testSwiftCSS.size(selector: "#View", key: "size") //CGsize

//1.Get CSS file path
let path = Bundle.main.url(forResource: "cssFileNmae", withExtension: "css")
//2.Get parsed CSS
let css = SwiftCSS(CssFileURL: path)
//3.Use it
let width = css.int(selector: "#View", key: "width")

public let SwiftDeviceCss = SwiftCssStyleSheet.deviceCss()

class SwiftCssStyleSheet {
    
    private enum ScreenSize {
        case _320_480 //iPhone4 etc.
        case _320_568 //iPhone5 etc.
        //iPhone6....
    }
    
    static private let screenSize: ScreenSize = {
        let screen = UIScreen.main
        let size = UIScreen.main.fixedCoordinateSpace.bounds.size
        switch (size.width,size.height) {
        case (320,640):
        	return ._320_480
        //......
        }
    }()
    
    static func deviceCss() -> SwiftCSS {
        switch self.screenSize {
        case ._320_480:
            return SwiftCSS(CssFileURL: URL.CssURL(name: "iPhone4"))
        case ._320_568:
            return SwiftCSS(CssFileURL: URL.CssURL(name: "iPhone5"))
        //......
        }
    }
    
}

view.frame.size = SwiftDeviceCss.size(selector: "#View", key: "size")

public class SwiftCssTheme {
    
    public static let updateThemeNotification = Notification.Name("SwiftCSSThemeUpdate")
    
    public enum Theme {
        case day
        case night
    }
    
    public static var theme: Theme = .day {
        didSet {
            switch theme {
            case .day:
                self.themeCSS = SwiftCSS(CssFileURL: URL.CssURL(name: "day"))
            case .night:
                self.themeCSS = SwiftCSS(CssFileURL: URL.CssURL(name: "night"))
            }
            NotificationCenter.default.post(name: updateThemeNotification, object: nil)
        }
    }
    
    public static var themeCSS = SwiftCSS(CssFileURL: URL.CssURL(name: "day"))
}

extension UIView {
    
    private struct AssociatedKeys {
        static var selector = "themeColorSelector"
        static var key = "themeColorKey"
    }
    
    var backgroundColorCSS: (selector: String,key: String) {
        get {
        	let selector = //Use objc_getAssociatedObject to get value.....
        	let key = //.....
            return (selector,key)
        }
        
        set {
            let selector = newValue.selector
            let key = newValue.key
            
            //Use objc_setAssociatedObject to set value......   
            
            NotificationCenter.default.addObserver(self, selector: #selector(_cssUpdateBackgroundColor), name: SwiftCssTheme.updateThemeNotification, object: nil)
            
            _cssUpdateBackgroundColor()
        }
    }
    
    private dynamic func _cssUpdateBackgroundColor() {
        self.backgroundColor = SwiftCssTheme.themeCSS.color(selector: self.backgroundColorCSS.selector, key: self.backgroundColorCSS.key)
    }
}

self.view.backgroundColorCSS = ("#View","color")

@IBAction func changeColor(_ sender: UIButton) {
    if SwiftCssTheme.theme == .day {
        SwiftCssTheme.theme = .night
    } else {
        SwiftCssTheme.theme = .day
    }
}