Its because you probably don't have a "container" for it. You need to have that code inside some other div tag that has something like
Code:
position: relative;
width: 500px;
height: 600px;
The position relative is important and so is having a set width. The reason it is looking different at different resolutions is because if you don't have a container around that code it is positioning itself using the top left corner of the browser window.
so in the end you'll have code thats like this (if your are putting all yoru css code inline:
Code:
<div style="position:relative;width:600px;height:600px;">
<div style="position:absolute;left:65px;top:60px;height :400px;">
</div>
</div>
Hope that makes sense, but I'm 100% sure thats what your problem is. Everyone learning CSS runs into that once.