Change Color of One Menu Page Tab

[mmafight]

Hello everyone,

I want to be able to change the color of one of my Menu tabs/pages, specifically the one that says "Shop" toward the top of the page. I'd like to make it stand out more, maybe make it red with white font.

My website is MMAFight.com and I used the Firefox Firebug to find out my class page item. So basically I added the following code at the very end of my Stylesheet in order to make my Menu Page "Shop" red, instead of that gray button I currently have:

#nav li.page-item-10164 {background: red;}

However, it doesn't seem to be working. I've read past threads, but none of them go in depth with it so that's why I opened up a new thread. The only button I want to change is "Shop" so if someone can help me out here, I'd greatly appreciate it.

Also, if I wanted to make a custom button instead to replace the "Shop" with something I can create, how would I be able to implement that instead?

Thx in advance everyone