CodeIgniter + Google App Engine - all links go to index page

Question

I am using Google App Engine for the first time. I am trying to upload a website which I have worked with CodeIgniter. I have successfully uploaded the website. But the problem is that whenever I click on a link it goes to the same index page, even the CSS and JS.

My app.yaml is pasted below:

application: xxxxx
version: 1
runtime: php
api_version: 1

handlers:
- url: /css
  static_dir: css/

- url: /js
  static_dir: js/

- ulr: /fonts
  static_dir: fonts/

- url: /
  script: index.php