[css] CSS: How to position two elements on top of each other, without specifying a height?

I had to set

Container_height = Element1_height = Element2_height

.Container {
    position: relative;
}

.ElementOne, .Container ,.ElementTwo{
    width: 283px;
    height: 71px;
}

.ElementOne {
    position:absolute;
}

.ElementTwo{
    position:absolute;
}

Use can use z-index to set which one to be on top.