Further to my previous query.
If I change a tag class in the HTML code directly. <p><b>words </b><p/> it will change straight away in book view to bold, or <p><em>words </em><p/> Italic etc.
However if I change it using the CSS it will NOT change until I reload Sigil and the book.
This is happening with every book I have tried it on.
Peace,
John P.