使用边距设置跨距之间的距离

Here is two spans(in real life a lot of spans) situated at the web page. I would like to set the distance betwwen them. I want to use margin-bottom attribute for this, but I can't see any affect of using it. The spans are still on the previous position. That is wrong. Here is my code:Here is two spans(in real life a lot of spans)