Update.

src/snek/static/njet.css

@@ -0,0 +1,18 @@
+
+/* CSS version */
+.njet-dialog {
+  position: fixed;
+  top: 50%;
+  left: 50%;
+  transform: translate(-50%, -50%);
+  padding: 20px;
+  min-width: 33px;
+}
+.njet-window {
+  position: fixed;
+  top: 50%;
+  left: 50%;
+  transform: translate(-50%, -50%);
+  padding: 20px;
+  min-width: 33px;
+}