Font size in post area

Once the message is posted the font size is fine.
It's when you're writing it out to be submitted.The font is just way too small and hard to read(an understatement)
Everything else on the forum is working just fine.Real pleased.
I look in the COLORS section.Nope.Not there.Checked out the CSS and not sure where the font size for this area is.
I don't want to make a mistake in CSS.Could make matters worse if i do this wrong.
So how do i change this font size and where?
HELP! Sure it's a simple thing to fix.

Whats your forum version? Also is this in the quick reply or advanced posting ?

take a look.I changed the font size and it shows up in most areas.
But you put up a post and after you submit-it is ant size print.Some of us older people simply can't see this size.
THE FORUM
I would call this the message area.Not sure if that's the correct term but you can see the small size of the font when you read the posts.
Not when you type the message up.There it's fine.
i'm not sure what version this is.Where do you check?

can you post a screenshot of it?

Admin Panel>Display
Then you will see theme version.

phbb2

Code:

.postbody{
    font-size : 20px;
    }

Add this to your css, change the 20 to whatever you want.