Add "numbers" skin

icons/skins/numbers/7.svg

+<?xml version="1.0" encoding="UTF-8"?>
+<svg enable-background="new 0 0 100 100" version="1.1" viewBox="0 0 100 100" xml:space="preserve" xmlns="http://www.w3.org/2000/svg"><rect width="100" height="100" ry="2" fill="none"/><rect width="100" height="100" fill="#c5c5c5" stroke="#000" stroke-linecap="round" stroke-linejoin="round" stroke-opacity=".5" stroke-width="2.6"/><g aria-label="7"><path d="m80.33 6.47v7.08q0 3.12-0.72 5.04-0.66 1.92-1.32 3.24l-31.68 66.18q-1.2 2.28-3.24 3.9t-5.52 1.62h-12l32.46-64.62q1.2-2.28 2.46-4.14t2.82-3.54h-40.14q-1.44 0-2.64-1.14-1.14-1.14-1.14-2.58v-11.04z"/></g></svg>

icons/skins/numbers/8.svg

+<?xml version="1.0" encoding="UTF-8"?>
+<svg enable-background="new 0 0 100 100" version="1.1" viewBox="0 0 100 100" xml:space="preserve" xmlns="http://www.w3.org/2000/svg"><rect width="100" height="100" ry="2" fill="none"/><rect width="100" height="100" fill="#c5c5c5" stroke="#000" stroke-linecap="round" stroke-linejoin="round" stroke-opacity=".5" stroke-width="2.6"/><g aria-label="8"><path d="m50 94.49q-6.84 0-12.48-1.8-5.64-1.86-9.66-5.16-4.02-3.36-6.24-8.1t-2.22-10.56q0-7.44 3.6-12.72 3.6-5.34 11.52-7.98-6.18-2.7-9.24-7.56-3-4.86-3-11.58 0-5.04 2.04-9.3 2.04-4.32 5.7-7.44 3.72-3.18 8.82-4.98t11.16-1.8 11.16 1.8 8.76 4.98q3.72 3.12 5.76 7.44 2.04 4.26 2.04 9.3 0 6.72-3.06 11.58t-9.18 7.56q7.86 2.64 11.46 7.98 3.66 5.28 3.66 12.72 0 5.82-2.22 10.56t-6.24 8.1q-4.02 3.3-9.66 5.16-5.64 1.8-12.48 1.8zm0-12.66q3.42 0 5.94-1.02 2.58-1.02 4.26-2.76 1.68-1.8 2.52-4.2 0.84-2.46 0.84-5.28 0-6.48-3.36-10.02-3.3-3.6-10.2-3.6t-10.26 3.6q-3.3 3.54-3.3 10.02 0 2.82 0.84 5.28 0.84 2.4 2.52 4.2 1.68 1.74 4.2 2.76 2.58 1.02 6 1.02zm0-39.66q3.42 0 5.64-1.08t3.54-2.88 1.86-4.08q0.54-2.34 0.54-4.8 0-2.28-0.66-4.38t-2.1-3.66q-1.38-1.62-3.6-2.58-2.16-0.96-5.22-0.96t-5.28 0.96q-2.16 0.96-3.6 2.58-1.38 1.56-2.04 3.66t-0.66 4.38q0 2.46 0.54 4.8 0.54 2.28 1.86 4.08t3.54 2.88 5.64 1.08z"/></g></svg>

lib/provider/data.dart

@@ -7,7 +7,7 @@ class Data extends ChangeNotifier {
   List _availableLevelValues = ['easy', 'medium', 'hard', 'nightmare'];
   List _availableSizeValues = ['small', 'medium', 'large', 'extra'];
   List _availableColorsValues = ['5', '6', '7', '8'];
-  List _availableSkinValues = ['default', 'retro', 'symbols'];
+  List _availableSkinValues = ['default', 'retro', 'numbers', 'symbols'];
 
   List get availableLevelValues => _availableLevelValues;
   List get availableSizeValues => _availableSizeValues;