Display in red the confirm buttons of delete processes

cf https://github.com/yohanboniface/django-leaflet-storage/issues/34

youmap/static/youmap/youmap.css

@@ -70,4 +70,12 @@ input:-moz-placeholder, :-moz-placeholder {
 }
 #storage-ui-container select {
     margin-bottom: 10px;
-}
+}
\ No newline at end of file
+
+#storage-ui-container.warning .button {
+    background-color: #c60f13;
+    border: 1px solid #7f0a0c;
+}
+#storage-ui-container.warning .button:hover {
+    background-color: #970b0e;
+}