Here is the flex-box approach:
CSS
.parent {
display:flex;
height:100vh;
}
.child{
flex-grow:1;
}
.left{
background:#ddd;
}
.center{
background:#666;
}
.right{
background:#999;
}
HTML
<div class="parent">
<div class="child left">Left</div>
<div class="child center">Center</div>
<div class="child right">Right</div>
</div>
You can try the same in js fiddle.