Add subtle poker table green gradient background to game area

Author: Top-5

src/App.css

@@ -81,7 +81,13 @@ h1 {
 }
 
 .game-area {
-  background: rgba(255, 255, 255, 0.1);
+  background: linear-gradient(135deg, 
+    #1a5632 0%, 
+    #2d7a4d 25%, 
+    #1f6840 50%, 
+    #2d7a4d 75%, 
+    #1a5632 100%
+  );
   border-radius: calc(var(--unit) * 0.006);
   padding: calc(var(--unit) * 0.01);
   width: calc(var(--unit) * 0.98);
@@ -90,6 +96,8 @@ h1 {
   flex-direction: column;
   flex: 1;
   max-height: calc(var(--unit) * 0.94);
+  box-shadow: inset 0 calc(var(--unit) * 0.002) calc(var(--unit) * 0.008) rgba(0, 0, 0, 0.3),
+              0 calc(var(--unit) * 0.004) calc(var(--unit) * 0.012) rgba(0, 0, 0, 0.2);
 }
 
 .top-row {