Overwriting CSS Classes

I’m somewhat of a newb when it comes to CSS, but I’m having trouble understanding the parameters for overwriting CSS on an incoming iFrame page (if that’s fully possible).

The URL that I’m bring in has a table and within that table data that I’d like to format differently:

<span class=”date”>5/16/2013</span>

and

link name

I’d like to be able to override the CSS that’s coming from their URL with CSS from my site.

Not sure if it helps/hinders, but the iFramed content is a sub-domain of the main URL (i.e. https://www.domain.com (primary URL), sub.domain.com (iframed content))

Could you explain if this is possible with the shortcodes? I’ve read the Advanced iFrame settings page and not quite getting a clear picture on what shortcode I need to use and what content to put in them.

Thank you!

https://www.ads-software.com/extend/plugins/advanced-iframe/