Proportionally resize width and height of div on window resize

by vishnu nagarajan

HTML

<div class="parent">
   <div class="child">
        something...
   </div>
</div>

CSS

.parent {
    position: relative;
    width:1280px;
    max-width: 100%;
    margin: 0 auto;
    padding: 30px;
}
.parent:before {
    margin-top: 25%;
    content: '.';
    font-size: 0;
    display: inline-block;
}
.child {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    background-color: red;
    max-height: 100%;
}