Yesterday I did a silly mistake. I misunderstand CSS Comma Syntax.
This is the original edited code.
I looked at it carefully and debugged using Firebug. I mentioned the div class, entry-content, for the paragraph. Why it is still affecting the header paragraph? After I split the CSS code, I understand it clearer.
The code below is the correct solution. I should mention the div class, entry-content, for every tags after the commas. So sometime, short cut syntax can cause more mistaken occurred.