UIWebView CSS injection using JavaScript

I'm trying to inject a local css file into an UIWebView that finished loading website such as google etc.

I'm trying with JavaScript but with no success.

- (void)webViewDidFinishLoad:(UIWebView *)webView {
    NSString *cssPath = [[NSString alloc] initWithString:[[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"styles.css"]];
    NSURL *baseURL = [NSURL fileURLWithPath:cssPath];

    NSString *js = [NSString stringWithFormat:@"var fileref = document.createElement('link');
                    fileref.setAttribute('rel', 'stylesheet');
                    fileref.setAttribute('type', 'text/css');
                    fileref.setAttribute('href', %@);", baseURL];

    [webView stringByEvaluatingJavaScriptFromString:js];
}

Thanks,