Untitled

<body>
    <header></header>
    <main>
        <section>
            <section class="innersection">
            some content
            </section>
            <aside class="sidebar">
            snas
           </aside>
        </section>
    </main>
    <footer></footer>
</body>

main{
    width: 100%;
    min-height: 800px;
}

.innersection{
float:left;
width:94%;
display:inline;
}
.sidebar{
float:right;
width:5%;
display:inline;
}