I'm pretty new to ebooks, HTML and the PRS-505 so I wonder if someone could help or point me in the right direction. I am very much in the explore-and-find-out-what-works stage at the moment.
To tidy up MSWord's generated HTML, I wanted to extract all the style info into a re-usable CSS file. The HTML plus linked CSS loads fine in my browser.
When I upload to calibre the HTML and CSS file get zipped into a single file in the normal way. However, when I convert to LRF or EPUB the styling in the CSS doesn't seem to be used.

Could one of you experts please tell me whether this is what you would expect or make a suggestion what I might be doing wrong? I can force the CSS to be used by using the ConvertEbooks/Look&Feel/ExtraCSS option to point at a copy of the CSS file on my C: disk but I had hoped to use this option as a style 'tweaker' rather than for the whole lot.
FYI I have tried unzipping calibre's zip file to make sure the HTML and CSS still function as a pair after the upload. They seem fine. I've also tried copying the CSS content back into the HTML file and re-uploading that as a single file. That works fine as well.
I also know I could forget about HTML/CSS and just upload the MSWord file as RTF. I don't do this because of the formatting which seems to be lost using RTF (centre- & right-alignment, line breaks etc), and anyway where would be the fun in that!
Any enlightenment would be appreciated. Who knows, one of these days I might actually get round to reading a book on my shiny new SonyReader!