Q:

How to make font-size relative to container size

HTML:
<span> text </span>

CSS:
span{
  width: 200px;
  height: 200px;
  display: inline-block;
}

I would like to make text fit the size of the span.  So if the span is 200x200, font should have like 72px height.  If it's smaller, font-size should me smaller.  Is this possible? 
Setting a font size in percentages doesn't seem to have any effect. 

A:

I think using the em unit for height and font size is the best choice for the problem.  I can't give the exact code, But Do this reading, it awesome and better for your future design. 
http://www.w3.org/WAI/GL/css2em.htm

