Thanks much. This is perfect! I didn't realize there was this capability (ain't Calibre great? Great instincts, Kovid, to think of making every little thing so open). I've since found the CSS sticky post in this Calibre forum, which tells me I can make permanent changes within the View window Preferences (I had originally only found some place to alter CSS under "Conversion").
P.S. I actually started to write the post inclusively for Win, Mac, and Linux, but gave up on my searches for "Kindle for Mac" and "Kindle for Linux," and hoped I'd get the slack non-North Americans give the U.S. posters for their U.S.-centric posts.