Hi Arthur,
Your problem is simple... your bottom margin!
For DIV you've created, you are using this to center your pages:
<div style="margin: 10px 100px;">
That translating to: side margins 100px, top and bottom to 10px.
But the bottom margin create this gap! Then, instead use this:
<div style="margin: 10px 100px 0px 100px">
This will solve your problem.
Best Regards,
Jacques