Support a FlashCard before showing the notes that comprise a chord

My much anticipated feature: first prompt the user for a name of a chord, then
show the user that chord.

Cascading changes:
I changed the "Tap to practice" overlayButton's opacity from 30% to 100% because
pausing when showFlashCard is True causes the two piece

TIL:
You can batch Elm Subscriptions using the Sub.batch function.

What I haven't learned yet:
How to best handle rotating screens for mobile devices (i.e. portrait
vs. landscape modes). In time...

What's left?
- Support sound
- Support a fine-tune section of the preferences
- Support tablet and web browser variants
- Ask users for the "I chord" instead of asking "C major Root position"
- More styling (of course)

website/sandbox/learnpianochords/src/FlashCard.elm

@@ -0,0 +1,42 @@
+module FlashCard exposing (render)
+
+import Html exposing (..)
+import Html.Attributes exposing (..)
+import Html.Events exposing (..)
+import Responsive
+import State
+import Tailwind
+import Theory
+
+
+render :
+    { chord : Theory.Chord
+    , visible : Bool
+    }
+    -> Html State.Msg
+render { chord, visible } =
+    let
+        classes =
+            [ "bg-white"
+            , "fixed"
+            , "top-0"
+            , "left-0"
+            , "z-30"
+            , "w-screen"
+            , "h-screen"
+            , Tailwind.if_ visible "opacity-100" "opacity-0"
+            ]
+    in
+    button
+        [ classes |> Tailwind.use |> class ]
+        [ h1
+            [ [ "text-center"
+              , "transform"
+              , "-rotate-90"
+              , Responsive.h1
+              ]
+                |> Tailwind.use
+                |> class
+            ]
+            [ text (Theory.viewChord chord) ]
+        ]