[css] how to avoid extra blank page at end while printing?

First, emulate the print stylesheet via your browser's devtools. Instructions can be found here.

Then you'll want to look for extra padding, margin, borders, etc that could be extending the dimensions of your pages beyond the 8.5in x 11in. Pay special attention to whitespace as this will be impossible to detect via the print preview dialog. If there is whitespace that shouldn't be there, right-clicking and inspecting the element under the cursor should highlight the issue (unless it's a margin causing it).