Don't forget to close your HTML tags
sewingandembroiderywarehouse.com
sewingandembroiderywarehouse.com
Not very pretty.
This means that if you set your font-size to 1.5em, and you have an element inside (as a result of the unclosed tag) also set to 1.5, the one inside is set to 1.5 times that size (or 2.25 of the original 1em). That cascades on and on and on and...
EDIT: And yes, the heading tags have relative font sizes, as cleverjake pointed out.