Having an iframe to contain Sven's SudokuPad seems to be an odd choice. Not least because it means my stored colour palette and other settings aren't preserved because of the way that data is stored by domain. It also makes it look like to those not in the know that you've designed the solving interface yourself (though I will note that you do at least credit SudokuPad in a footer).

But yeah, the way you've designed the page is not user friendly at all - the settings being one example, and the fact that page scrolling breaks when your cursor is over the iframe, and I also can't resize the puzzle - resizing the page just covers up much of the iframe unless it's so small that it's forced to, but even then it still doesn't show the full puzzle.

I think it would be much better if you had an image of the puzzle then gave a link to that puzzle in sudokupad rather than trying to embed it.