Hi Arthur,
Nice addition to your site, I haven't see that one before (sun and moon phase)!
Your problem is that you haven't put "spacers" in the right place.
Instead of margin in inner Div, put padding in outer Div (class="box3-1").
Also, you could play with width of you picture iframe actually is 100%
but could be much smaller, as it isn't 100% of needed space, but 100% of
available space! <iframe id="earth-moon" width="100%" ....
Hope this help!
Regards,
Jacques