How to make a div sitting on the bottom of another div with an unknown height of one of them


I have these divs:

<div class='jama'>
    <div class='prispevky'> Blogger posts, photos and so one. So I don't know the height of this div. </div>

The problem is, that the outer div called "jama" has to be 400px or more tall:

.jama {
        width: 488px;
        background-image: url(&quot;;);
        background-position: top;
        background-repeat: no-repeat;
        margin: 0 auto;
        min-height: 400px;

Is there a way how to make the div called "prispevky" always on the bottom of the div called "jama"?

Set position:relative on .jama, then on .prispevky set position:absolute and bottom:0;left:0;right:0;