Instead of eliminating the font-sizes, change them to a relative measure like em - 1em for the body. 1.15em or 1.2em for the title and subtitle, and 0.6em for the colophon. This will allow the readers to change the font sizes while preserving the look of the different sizes used.
In general, relative units are a better choice for fonts and indents, but absolute sizes work best for margins - but that's my opinion, I'm sure others may disagree.
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