You can also use CSS3 flexbox
layout, which is well supported nowadays.
.container {
display: flex;
flex-flow: row nowrap;
justify-content: space-between;
background:black;
height:400px;
width:450px;
}
.left {
flex: 0 0 300px;
background:blue;
height:200px;
}
.right {
flex: 0 1 100px;
background:green;
height:300px;
}
See Example (with legacy styles for maximum compatiblity) & Learn more about flexbox.