How to get CSS to target new nodes being inserted? I am customizing nodes for a blog entree's so they have a certain aesthetic look to it. However, I ran into a problem. 

I can enter custom CSS code to style the nodes for already existing ones and set them with classes, but if someone is going to create a new node on the site, the blog CSS doesn't appear because I have to go in to each one and constantly hand-code it.

Obviously this is time-consuming and not the right way to go about it, because anyone who creates a blog would have to wait for me to style it for them. Is there a way where I can make a CSS code that will keep the look and feel every time someone creates a new blog entree?
I'm not sure I get the scenario.
What if you apply your css to both old and new classes?

Example

.old_nodes .content, .new_nodes .content {
   color:red;
} 


This will give same style to both new and old nodes.