Hi,

the iframe module uses the template component layout to render contents, commonly done in Joomla using the query string param '?tmpl=component'
If you want to style contents inside the iframe from the jsitemap component, you have 2 choices:

1. Check CSS files loaded by your template for the component layout, and check if your template has the file component.php supporting it. Probably a subset of CSS files will be loaded and you can pick one of them to customize.

2. Perform a full template override for the component layout as explained in the PDF docs at the paragraph 'Override HTML sitemap layout', this can apply to both HTML and CSS files.

Cheers,
John