stretching panels in a fixed height parent block

by audetwebdesign

HTML

<div class="A parent">
    <div class="A a1">a1</div>
    <div class="A a2">a2</div>
    <div class="A a3">a3</div>
</div>

CSS

.A {
    width: 100%;
}
.parent {
    height: 300px;
    width: 300px;
    position: relative;
}
.a1 {
    height: 100px;
    background-color: pink;
}
.a2 {
    height: 100px;
    background-color: beige;
}
.a3 {
    background-color: yellow;
    position: absolute;
    top: 200px;
    bottom: 0;
}