For even more granularity, the Book Browser and Table of Contents QDockWidgets can be accessed individually with the .BookBrowser and .TableOfContents selectors (notice the preceding "." ).
Thus the Book Browser's fonts can be styled with:
Code:
.BookBrowser QTreeView { font-size: 10pt; }
And the Table of Contents fonts with:
Code:
.TableOfContents QTreeView { font-size: 8pt; }