diff --git a/flash.css b/flash.css
index 7898192..0e772f1 100644
--- a/flash.css
+++ b/flash.css
@@ -1 +1,28 @@
-a
+body {
+    font-family: Arial, sans-serif;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    height: 100vh;
+    margin: 0;
+}
+
+#flash-container {
+    text-align: center;
+}
+
+#number-display {
+    font-size: 48px;
+    margin: 20px;
+}
+
+#result {
+    font-size: 24px;
+    margin-top: 20px;
+}
+
+/* 白文字用のクラス */
+.white-text {
+    color: white;
+}