style.css file not responding to changes-SOLVED

"Thanks in advance.

I'm trying to change "inner padding" width from 48px to 18px to make my posts wider.
I can see the changes made on my copy of style.css on my localhost (my web is not yet online) but when
I look at my pages with firebug the old padding width of 48px remains.

What gives?
HOW do I make these changes permanent and WHY is this happening?
Am I changing the wrong settings in the wrong file? Are these settings controlled from an external source that I don't have access to?

.inner {
padding: 25px 48px 20px;
}"

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After some research I discovered that I was trying to "Hack the Core" which I just concluded is waaaaaay bad.
I'm now researching other modules that will accomp my task.
Hope this helps some other poor slob.