Put one DIV in center of another DIV using CSS example

Hi

I have 2 div in my page div1 and div2

below is css:

#div1 {
    width: 5000px;
    height: 228px;
    background: url(../Image/Main/mainback.png) repeat;
    background-size: 33px;
    text-align: center;
}
#div2 {
    width: 1349px;
    height: 15px;
    background: url(../Image/Main/toplamp.png) no-repeat;
}

I want div2 be at the center of Div1how I can do it?

best regards

Neda