how do you define the heading size in css code example

Example: css h sizes

h1  =>    32px    (2em)
h2  =>    24px  (1.5em)
h3  =>  20.8px  (1.3em)
h4  =>    16px    (1em)
h5  =>  12.8px  (0.8em)
h6  =>  11.2px  (0.7em)