Keep div at the bottom of another div – css

#copyright {
    position: absolute;
    bottom: 0;
}
#outer {
    position: relative;
}

This will have the unfortunate side effect though that #copyright does not count towards the height of #outer anymore, in your example #outer would be 0px high. You can add a bottom-padding to #outer if you’re working with fixed heights.

#copyright {
    position: absolute;
    bottom: 0;
    height: 200px;
}
#outer {
    position: relative;
    padding-bottom: 200px;
}