SOURCE

<div class="box">
    <div class="box1"></div>
    <div class="box2">
        <div class="box3"></div>
    </div>
</div>

.box{
    width: 200px;
    height: 500px;
    background: red;
    display: flex;
    flex-direction: column
}

.box .box1{
    width: 100%;
    height: 100px;
    flex-shrink: 0;
    background: greenyellow
}

.box .box2{
    width: 100%;
    height: 0;
    flex-grow: 1;
    background: blanchedalmond
}

.box2 .box3{
    width: 100%;
    height: 100%;
    background: firebrick
}