This happens because you use position:relative on the #previous and #next elements. Like this they are repositioned but still use up the space they would originally occupy.
Use the following css instead:
.block-wapper {
position:relative;
...
}
#previous {
position: absolute;
left: 10px;
...
}
#next {
position: absolute;
right: 10px;
...
}
4
solved How to get rid of hidden space HTML/CSS [closed]