need a pdf with "appropriate" header size

Hi there,
I am having some issue in converting an epub file to a pdf file (for computer) with an appropriate Header size. I have played around with settings and everything is ok with the text size, but the chapter headers seems resilient
I am using Calibre
(CSS as follows
body {
font-family:Times New Roman, Georgia, serif;
margin-top:50px;
margin-bottom:50px;
margin-left:50px;
margin-right:50px;
}
Output file as A4 /12px (predefined fonts) / 8px (fixed spacing fonts)


Here is the pdf


and here is the original as seen with an eReader app in my desktop




Any hint?
:thanks: