silverstripe-framework/admin/templates/SilverStripe/Admin/Includes/LeftAndMain_MenuToggle.ss

<button class="sticky-toggle" type="button" title="Sticky nav"><%t LeftAndMain.MenuToggleStickyNav "Sticky nav" %></button>
<span class="sticky-status-indicator"><%t LeftAndMain.MenuToggleAuto "Auto" %></span>
<a class="toggle-expand" href="#"><span>&raquo;<span class="sr-only"><%t LeftAndMain.MenuToggleExpand "Expand panel" %></span></span></a>
<a class="toggle-collapse" href="#"><span>&laquo;<span class="sr-only"><%t LeftAndMain.MenuToggleCollapse "Collapse panel" %></span></span></a>