Styling the RSS Feed (having issues, help please)

Hello,

I hired someone to design our WordPress Blog to match the rest of the site.

However, I dont think this guy setup RSS styling. For some reason, sometimes when I load the RSS Feed, it appears styled. Other times when I load it in firefox, it is unstyled. When that happens, I get this message: “this xml file does not appear to have any style information associated with it. the document tree is shown below.”

Here is the RSS feed:
https://www.gem-tech.com/blog/?feed=rss2

How can I set it up, so it always appears styled, no matter which browser?

I tried to set it up so it calls a CSS file, but I have no idea where to put the CSS call, as I don’t know which files on the server contain the RSS feed information

Please help, thanks