[slowsmile]

I can confirm what DiapDealer has said. I've been playing around and altering some values in the qss file. I've discovered that it's just not possible to change any styling in Book View which is dim and almost unreadable when you use QDarkStyleSheet. And in HTML View you can only change a few styles for just the book text like background color, foreground color and font styles. But you cannot alter the styling of any of the xml or doctype headers or html tags or anything alse. So this greatly limits what you can actually do to style your document.

See example thumbnail below where I've changed just the background color, text color and some fonts(based on QDarkStyleSheet) in Sigil's main tab frame by altering a couple of style properties in the qt_styles.qss stylesheet.