Gonna answer myself, because this solution actually covers my needs of it being "as a html element should be, and can resize etc", even though I developed this solution from Grants answer.
http://jsfiddle.net/Wkk7W/6/
Set the element to position:absolute
, then give it a pseudo element with:
content: "";
display: block;
position: absolute;
top: 0;
width: 102%;
margin: -1px 0 0 -1%;
height: 102%;
background: black;
z-index: -1;
This way it keeps the elements width and height, z-index: -1 to put it behind the text. It might not require the display:block, i didn't check.
There are still a few tiny gaps but they are basically impossible to cover and I am happy with it the way it is.