Have you checked the classes on your <body> element?
It depends on the theme but WordPress has a function
body_class()
that dynamically adds a bunch of useful classes in there. It may look like this:
<body class="archive category category-news category-2 two-column content-sidebar">
As you can see it is a powerful helper as you can easily accomplish complex style changes by prepending your definitions with these classes. In your case it could be:
.category-something .entry-meta {
/* whatever style changes you need */
}
If there is no such awesomeness in your <body> element then you can add it there yourself very easily:
<body <?php body_class(); ?>>
The answer provided by @xLRDxREVENGEx is certainly valid and points in the right direction. It’s certainly worth (re)thinking what approach is the right one for your use case.
Hope this helps!