Make the menu buttons opaque

The translucent panel fill was invisible on the list screens, which sit on
flat ink, and wrong on the splash: the court's white lines ran straight
through STATS and RANKINGS and the buttons stopped reading as buttons.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

index.html

@@ -151,8 +151,11 @@
            font-style: normal; letter-spacing: 1px; }
   .fig.bad i { color: var(--bad); }
   /* one button look for every menu screen */
+  /* OPAQUE, not the translucent panel fill. On the list screens it makes no visible difference —
+     they sit on flat ink — but on the splash a see-through button lets the court's white lines run
+     straight through the lettering, and the button stops reading as a button. */
   .btn { display: block; width: 100%; margin: 0 auto 10px; padding: 12px 10px;
-         background: var(--panel); border: 2px solid var(--line); color: var(--cream);
+         background: var(--solid); border: 2px solid var(--line); color: var(--cream);
          font: 400 12px Silkscreen, monospace; letter-spacing: 1px; cursor: pointer;
          -webkit-tap-highlight-color: transparent; }
   /* The generated button plates are gone with the tutorial. The primary is a flat crimson block