css.php modified as:
h1 { font-size: 16px; line-height: 1.2; margin: 0.3em 0 10px; font-weight: bold;}
h2 { font-size: 10px; line-height: 1.3; margin: 1em 0 .2em;font-weight: bold; text-decorationverline; color:#A38EA1;}
h3 { font-size: 6px; line-height: 1.3; margin: 1em 0 .2em; font-weight: bold; text-decoration:underline; color:#081B78;}
h4 { font-size: 5px; margin: 1.33em 0 .2em;font-style: italic;} }
h5 { font-size: 1.0em; margin: 1.67em 0; font-weight: bold;color:#008000;}
h6 { font-size: 0.9em; margin: 1.67em 0; font-weight: bold; }

font weight, colors are well changed but font-size remain as default: 34, 28, 24px...

Where can i change it?

Thank you

Why would you edit the theme file? Look in the themes 'CSS Inserts' option

Thank you. It works fine now.
I'm upgrading my site from Atahualpa 3.4 and i never use this option before.

Best regards