Just to show I have read the manual - the manual states:-
The base font size of a document is the most common font size in that document, i.e., the size of the bulk of text in that document. When you specify a Base font size, calibre automatically rescales all font sizes in the document proportionately, so that the most common font size becomes the specified base font size and other font sizes are rescaled appropriately.
I have been converting some HTML files to ePub with a specified Base of 18pt. (my eyesight is not as good as it was).
When the file is converted I find that in the CSS the "Calibre" class?/style? contains an 'em' size equivalent to 18pt and that the Body tag in the main files contain refer to "Calibre".
The problem is that the bulk of the text is controlled by a different class?/style? (e.g. "Calibre1") which is usually '1em'. I have been manually amending this font size but from the above quote this should not be necessary.
Following a tip I found in another thread I changed the Font size key values to 16pt, 16pt, 18pt, 20pt, 22pt 24pt. After converting another file and found no difference. I use the generic ereader profiles for input and output.
What have I missed and need to learn?