Update static/app.css

static/app.css

@@ -13,7 +13,11 @@ html, body {
     display: flex;
     flex-direction: column;
 }
-
+/* Drag & Drop Feedback */
+.drag-active {
+  background-color: rgba(0, 150, 255, 0.1) !important;
+  border: 2px dashed #1ec9f3 !important;
+}
 /* Header */
 header {
     flex: 0 0 17vh;