Burp doesn't intercept localhost

I'm new to burp and is playing around to intercept traffic from my localhost machine (website that I created for testing). However I noticed that burp intercept the css rather that traffic/url. What do I do to make burp intercept my localhost/php request?

My firefox/burp are all configured to 127.0.0.1:8080 as per localhost setting.

In Burp go to Proxy -> Options -> Proxy listeners, and confirm the Running box is ticked.

1. In proxy tab make sure intercept is turned off.

2. Make sure the proxy in burp listener is 127.0.0.1:6666.

3. Configure your browser to use 127.0.0.1:6666 as its proxy.

4. Configure Burp to use your original LAN proxy (from your original browser configs) as its upstream proxy.

5. Run your browser and access your application.

Additional reasons could be browser restricted ports. You mentioned you are using Firefox so Try this:

1. Type the following into Firefox address bar about:config

2. Type the following settings network.security.ports.banned.override

3. Enter your port number 6666