<div class="parent">
    <div class="child"></div>
</div>
.parent {
    display: flex;
    height: 400px;
    background-color: #222;
    flex-direction: column;
}

.child {
    background-color: red;
    width: 100px;
    height: 100px;
    margin-top: auto;
}
View Compiled

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.