A great new book called the CSS Detective is awesome. One sentence explanations with code examples of all the general problems with positioning, floats etc and then, there are four/five case studies with all the code for you to look and figure what's wrong all before the explanations.
Now, as to your issue, are you using positioning at all or just floats? Though floats were not intended for layout, they've become a huge tool for just that but there are caveats just as there are for other.
A child will inherit its parents properties unless overridden.
Sounds like if you're using floats, you would float the item left/right and stick a margin-left or right of 50px. If absolute positioned, then just check the onscreen coordinates and use left: and top: with px as to where to put it.
Obviously, you have to have a parent or container with position:relative which wraps the element you position absolutely as that is the item the element/child will get positioned against.
Relative establishes a positioning concept/target. But, it's 'relative' to its own position within the document flow.