Render a mobile-friendly piano

For now since I'm the only customer and I'm primarily making this for myself,
I'm styling the app specifically for my Google Pixel 4. If I find this app
useful, I will consider supporting other devices.

I'm using the Icons that I bought when I purchased the "Refactoring UI" book.

Other news:
- I bought the domain learnpianochords.app!

What's left:
- Style the "fine tune" tab of the preferences view
- Better support non-mobile devices like the browser and tablet devices
- Deploy the application to learnpianochords.app
- Redesign the "key" tab of the preferences view to sort the keys according to
  the circle of fifths
- Dogfood
- Simplify until I cannot simplify anymore

website/sandbox/chord-drill-sergeant/src/Icon.elm

@@ -0,0 +1,44 @@
+module Icon exposing (..)
+
+import Svg exposing (node, svg)
+import Svg.Attributes exposing (..)
+import UI
+
+
+svgColor color =
+    let
+        classes =
+            case color of
+                UI.Primary ->
+                    [ "text-gray-500", "fill-current" ]
+
+                UI.Secondary ->
+                    [ "text-gray-300", "fill-current" ]
+    in
+    class <| String.join " " classes
+
+
+cog =
+    svg [ class "icon-cog", viewBox "0 0 24 24", xmlLang "http://www.w3.org/2000/svg" ]
+        [ Svg.path
+            [ svgColor UI.Primary
+            , d "M6.8 3.45c.87-.52 1.82-.92 2.83-1.17a2.5 2.5 0 0 0 4.74 0c1.01.25 1.96.65 2.82 1.17a2.5 2.5 0 0 0 3.36 3.36c.52.86.92 1.8 1.17 2.82a2.5 2.5 0 0 0 0 4.74c-.25 1.01-.65 1.96-1.17 2.82a2.5 2.5 0 0 0-3.36 3.36c-.86.52-1.8.92-2.82 1.17a2.5 2.5 0 0 0-4.74 0c-1.01-.25-1.96-.65-2.82-1.17a2.5 2.5 0 0 0-3.36-3.36 9.94 9.94 0 0 1-1.17-2.82 2.5 2.5 0 0 0 0-4.74c.25-1.01.65-1.96 1.17-2.82a2.5 2.5 0 0 0 3.36-3.36zM12 16a4 4 0 1 0 0-8 4 4 0 0 0 0 8z"
+            , fill "red"
+            ]
+            []
+        , node "circle"
+            [ svgColor UI.Secondary, cx "12", cy "12", r "2" ]
+            []
+        ]
+
+
+close =
+    svg [ class "icon-close", viewBox "0 0 24 24", xmlLang "http://www.w3.org/2000/svg" ]
+        [ Svg.path
+            [ svgColor UI.Primary
+            , d "M15.78 14.36a1 1 0 0 1-1.42 1.42l-2.82-2.83-2.83 2.83a1 1 0 1 1-1.42-1.42l2.83-2.82L7.3 8.7a1 1 0 0 1 1.42-1.42l2.83 2.83 2.82-2.83a1 1 0 0 1 1.42 1.42l-2.83 2.83 2.83 2.82z"
+            , fill "red"
+            , fillRule "evenodd"
+            ]
+            []
+        ]