[O] Changing the font family in HTML export

[Dror Atariah]

Dear org mode users,

I'm trying to change the font used when exporting .org to .html. At the moment, 
I get 
"
<style type="text/css">
 <!--/*--><![CDATA[/*><!--*/
  html { font-family: Times, serif; font-size: 12pt; }
"
In the generated .html file. I would like to control this part, namely, I would 
like to have for example:
"
<style type="text/css">
 <!--/*--><![CDATA[/*><!--*/
  html { font-family: Helvatica, sans-serif; font-size: 12pt; }
"
Instead. I found several hints, but my emacs skill failed me, and I couldn't 
find a solution.

Can you help me? Thanks in advance,
Dror