Update index.html

index.html

@@ -53,7 +53,7 @@
           flex-direction: column; /* 縦に並べる */
           justify-content: center;
           align-items: center;
-          background-color: #000000;
+          background-color: #ffffff;
           border: 10px solid #000;
           border-radius: 10px;
           margin: 20px;