Update static/style.css

static/style.css

@@ -15,6 +15,12 @@ body {
     padding: 20px;
     text-align: center;
     width: 300px;
+    opacity: 1;
+    transition: opacity 0.5s ease-in-out;
+}
+
+.flashcard.fade-out {
+    opacity: 0;
 }
 
 .content {