Answer 1

I added to the CSS the following to the body tag:

padding:0;
margin:0;

You can also reset all paddings and margins to zero to have a proper box sizing all over the place using the universal selector like this:

* {
padding:0;
margin:0;
box-sizing:border-box;
}

box-sizing:border-box will make the padding and marging to fit exacty in the allocated space, meaning a div with a with of 100px and a marging of 10px will be 100px instead of 120px.

Then, your design class no longer needs the properties I see you used to attempt to fix the issue:
margin-right:-10px;
margin-left:-10px;
margin-top:-10px;

Give it a try, it worked for me.