giving margin between two divs?

In a page I have to display two div one on top and second under it (just like 开发者_开发问答showing something in a column). Requirment is to have 15px margin between two divs.

I tried to set top margin of second div and found the space between them but than top border of second div was gone. I even tried to set bottom margen of 1st div but again the result was same.

Why border of 2nd div disappears ? Please guide how space between them can be achieved without putting an empty div between them and also border of both should be there.

thanks for your guidance and support.

---

Use a reset css and try again. May be any content in these divs cause this issue.