Edit in JSFiddle

section {
    display: -webkit-flex;
}

div {
    -webkit-flex: 1;
    height: 200px;
    background: grey;
}

div:nth-child(2) {
    -webkit-flex: 2;
    background: yellow;
}

<section>
    <div></div>
    <div></div>
</section>