em - <fs 2em>Your own text in 2em</fs> Percent-Value 1em = Normal, 2em = double size
ex - <fs 2ex>Your own text in 2ex</fs> Percent-Value 1ex = Normal, 2ex = double size
% - <fs 200%>Your own text in 200%</fs> Percent-Value 100% = Normal, 200% = double size
px - <fs 12px>Your own text in 12px</fs> Not so good! px values may vary on different computers!
keywords - xx-small , x-small, small, medium, large, x-large, xx-large - <fs small>Your own text in small</fs>