Suggest you use Sigil for the epub editing job. It is more stable than Kompozer, made for job and has a lot of features that make things much easier.
With it you can make changes in the css and note the changes in book view.
Make sure that you do not have css at the top of each individual file that is governing this, or that there is in a stylesheet that is controlling everything. Calibre throws in a lot of its own styles which can be overlapping and hard to figure out. Some people just strip them all out in Sigil and take it from there.
It is possible to use Mobipocket Creator to create an html file from the pdf and then add the pages to a blank Sigil document. It will pull in all the associated pictures while it is doing that. The primary shortcoming to this method is that it does not keep the files in order, so it is necessary to drag them around in the book browser in Sigl to get them in order.