Edit in JSFiddle

<div id="cool">
    Cool
    <div id="warm">
        Warm
    </div>
</div>

#cool
{
    padding: 50px;
    height: 200px;
    width: 200px;
    background-color: rgba(0, 255, 255, 1);
}

#warm
{
    height: 200px;
    width: 200px;
    background-color: rgba(255, 0, 0, 1);
}