Main
Structure
The main section is a wrapper for the main site components .bl__header, .bl__body and .bl__footer. It has no styling applied as default.
When a sidebar is used, the .bl__main will get an offset to the sidebar with margin-left: $sidebar-width;. When the sidebar is collapsed on smaller viewports, the offset is removed to fill the viewport horizontally.
<main class="bl__main">
    <header class="bl__header">...</header> 
    <div class="bl__body">...</div>
    <footer class="bl__footer">...</footer>
</main>
