Please help me figure out class/div name for CSS customization


Please work from this page for this discussion:

So lets say for example I want to include custom CSS to change the font family, line spacing and other variables of the POST TITLES. (For example: "REAL LOVE MEETS REAL WORLD: LIKE CRAZY FILM REVIEW").

Here's what I do:
1) I open up google chrome and go to that page in chrome.
2) I put my cursor over the title, right click and select "Inspect Element". It then tells me a line with this: <h2 class="post-header">

Normally, what i would then do is write a line of code like this to put into my CSS custom:

.post-header {
font-family: "whatever"; }

HOWEVER, here is my problem:
1) When I do that, it changes that post header all over my site--I only want it to change it for that categories page.

Can someone please tell me what I need to figure out to be able to narrow down the thing I write in CSS custom to ONLY fit that title.

Let me clarify, I am looking for the instructions on how you figure out what the other name is for the div or class or whatever that will allow me to do this in several places on my site.

In other words, I'd like to change the font size of the top teeny menu WITHOUT CHANGING anything else. When I tried to do that I wound up accidentally changing things all over my site.

Tahnks in advance!