Edit in JSFiddle

<div class="container">
    <article>article</article>
    <nav>nav</nav>
    <aside>aside</aside>
</div>

* {
    outline: 1px solid pink;
}

.container {
    display: flex;
}

article {
    width: 60%;
    order: 2;
}
nav, aside {
    flex: 1;
    order: 1;
}

aside {
    order: 3;
}