Start e new post with a bigger font (default is too small)

I added custom style plugin,
I added these lines in it:

<style type=”text/css”>
font-family: verdana;
font-size: 18pt;
</style>

nothing changes, neither editing neither posting.
always tiny tiny font as in this post:

http://lnx.sinapsi.org/wordpress/2000/08/11/very-small-writings/

I’d like to change the default font of every post.
I suppose the paragraph font has to be changed.
I’d like to click on “add a new post” and start writing with, let say, verdana 18pt, then publish it and read it on my firefox as, let say, verdana 18pt.
That’s all.

I can display the fonts I like only if I, manually each time, add the html code, such as:
<p><font size=”5″>This font has been set manually changing the html code.</font></p>

I’d like not to change it manually, but having it already set as default font.

Excellent! You’re really helpful!