How to make reponsive CSS with ocsigen?

The best way to do that it to make one general css sheet plus three css sheets, small, medium and large screen.

Write theses lines in your css sheets:

@media only screen and (max-device-width: 480px)
@media only screen and (min-device-width: 481px) and (max-device-width: 768px)
@media only screen and (min-device-width: 769px)