For the parent
element, add the following properties:
.parent {
overflow: hidden;
position: relative;
width: 100%;
}
then for .child-right
these:
.child-right {
background:green;
height: 100%;
width: 50%;
position: absolute;
right: 0;
top: 0;
}
Find more detailed results with CSS examples here and more information about equal height columns here.