incerting into centred layers

having successfully followed other threads on here in respect of CSS centred layers and using

margin-left:auto;
margin-right:auto;

my problems start from here...

I insert inside this centred layer other layers to be fixed in postions

eg top: 10px left 10 px with 50px etc etc

and experimenting with different abasolute , relative etc i cannnot get them to appear in the exact position i require them to ? any pointers please?

kind regards

richard