refactor: prepare for adaptive background colors

Author: ACTCD

xcode/App-Mac/AppDelegate.swift

@@ -58,7 +58,9 @@ class AppDelegate: NSObject, NSApplicationDelegate {
 		window.titlebarAppearsTransparent = true
 		// Initialize webview
 		window.contentViewController = ViewController()
-		window.backgroundColor = .clear // DEBUG
+		// https://developer.apple.com/documentation/uikit/appearance_customization/supporting_dark_mode_in_your_interface#2993897
+		window.backgroundColor = NSColor(named: NSColor.Name("USBackgroundColor"))
+//		window.backgroundColor = .clear // DEBUG
 		window.center()
 		window.setIsVisible(true)
 		window.makeMain()

xcode/App-Shared/Shared.xcassets/Contents.json

@@ -0,0 +1,6 @@
+{
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

xcode/App-Shared/Shared.xcassets/USBackgroundColor.colorset/Contents.json

@@ -0,0 +1,38 @@
+{
+  "colors" : [
+    {
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "0x39",
+          "green" : "0x36",
+          "red" : "0x32"
+        }
+      },
+      "idiom" : "universal"
+    },
+    {
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ],
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "0x39",
+          "green" : "0x36",
+          "red" : "0x32"
+        }
+      },
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

xcode/App-Shared/ViewController.swift

@@ -39,7 +39,9 @@ class ViewController: PlatformViewController, WKNavigationDelegate, WKScriptMess
 		self.webView = WKWebView(frame: .zero, configuration: configuration)
 #if os(iOS)
 		self.webView.isOpaque = false
-		self.webView.backgroundColor = .clear
+		// https://developer.apple.com/documentation/uikit/appearance_customization/supporting_dark_mode_in_your_interface#2993897
+		self.webView.backgroundColor = UIColor(named: "USBackgroundColor")
+//		self.webView.backgroundColor = .clear // DEBUG
 //		self.webView.scrollView.isScrollEnabled = false
 #elseif os(macOS)
 		self.webView.frame = NSRect(x: 0, y: 0, width: 600, height: 600)