in js/drill.js [126:135]
$(".expand-toc-icon").on("click", function(){
// This relies on .sidebar's 'left' attribute...may be a cleaner approach
if($(".sidebar").css('left') == '0px'){
Drill.Docs._contractSidebar();
Drill.Docs._contractView();
} else {
Drill.Docs._expandSidebar();
Drill.Docs._expandView();
}
})