How to change the theme's font?
 

http://www.mysidiaadoptables.com/for...&pictureid=211

I decided to make a theme for my website myself. Because well...I have somewhat knowledge of CSS. However, I want to change the font of the entire website to one font. However, when I try to change the font, the font becomes weird and I don't know what to do anymore.

I'm editing the 'Main' theme.