It certainly does understand font settings, but your CSS is not correct:
font-size:18;
Is not legal CSS; try:
font-size:18
px;
Additionally, make sure you have the Trebuchet font on your system, as not all systems have it, and finally make the font declaration more explicit:
font-family:'Trebuchet MS';
Just using "font" is called the short hand syntax, but it's used for supplying more values:
http://www.w3schools.com/css/css_font.asp
Cheers.
Imar