Create a new wedesign to a site with old libraries

I was told to create a new webdesign to a website which I cannot change the HTML and JS. They only allowed me to change the stylesheet and images. So that's what I did. I spent the last 8 days optimizing the images creating sprites, joining css classes to make the page render faster... I did my best and did not touch the HTML and JS. So, today I was presenting my hard work to the company and they loved but their programmer told that their system has stopped working and there were a few messages in the console telling something went wrong. One of the messages which repeats a lot is

Line 2.906: Could not find selector ".side-bar" on the request to sitepor500.com.br. Check the manual.

I am VERY sure I did only change the CSS and images, nothing else. I am a webdesigner and not a programmer, so I ask you: is it possible to break the JS only changing the CSS? How can I fix this?

Thank you so much.