In CSS how do you change font size of h1 and h2

Question

In a word press twenty eleven theme. I want to change the size of headings When I wrap my headings around h1 and h2 tags as follows

My h1 heading          


        

Answer 1

 h1 { font-size: 150%; }
 h2 { font-size: 120%; }

Tune as needed.