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By making the chapters start on an odd page, the CSS processor might add blank pages to the previous page sequence as padding.

To style those blank pages add the following code in your customization css:

@page chapter:blank, table-of-contents:blank {
     @top-left      { content: none; }
     @top-center    { content: none; }
     @top-right     { content: none; }
     @bottom-left   { content: none; }
     @bottom-center { content: none; }
     @bottom-right  { content: none; }
}
Note: This just removes the headers and footers, but you can use a background image or a header with "Intentionally left blank" text.