I'm trying to make the bottom div fill the remaining height of the page, not just its parent div
body, html {
margin: 0px;
}
.top {
background-color: green;
width: 100px;
height: 50px;
}
.bottom {
background-color: red;
width: 100px;
height: 100%;
}
<div class="top"></div>
<div class="bottom"></div>