Artikel dan Sidebar Wrapper

CSS

#artikel-wrapper{float:left;width:68%;overflow:hidden}
#sidebar-wrapper{float:right;width:29%;overflow:hidden}
#sidebar{padding:5px}
.sidebar h2,.sidebar h3{color:#FFF;padding:4px 8px;background:#3384cc;margin:0;margin-bottom:5px}

Plus Responsive

@media screen and (max-width:600px) {
#artikel-wrapper{width:100%;float: none;}
#sidebar-wrapper{width:100%;float: none;}
}

HTML

Sidebar

<aside id='sidebar-wrapper'>
<b:section class='sidebar' id='sidebar' showaddelement='yes'></b:section>
</aside>

Artikel

Start

<aside id='artikel-wrapper'>

End

</aside>