add styles inline

app/assets/javascripts/sidebar.js.coffee

@@ -2,15 +2,14 @@ collapsed = 'page-sidebar-collapsed'
 expanded = 'page-sidebar-expanded'
 toggleSidebar = ->
-  $('.sidebar-wrapper').addClass('hide-sidebar')
   $('.nicescroll').getNiceScroll().remove()
+  $('.sidebar-wrapper').css('overflow-y','hidden')
   $('.page-with-sidebar').toggleClass("#{collapsed} #{expanded}")
   $('header').toggleClass("header-collapsed header-expanded")
   $('.toggle-nav-collapse i').toggleClass("fa-angle-right fa-angle-left")
   $.cookie("collapsed_nav", $('.page-with-sidebar').hasClass(collapsed), { path: '/' })
   setTimeout ( ->
-    $('.sidebar-wrapper').removeClass('hide-sidebar')
     $(".nicescroll").niceScroll(cursoropacitymax: '0.4', cursorcolor: '#FFF', cursorborder: "1px solid #FFF")
   ), 300

app/assets/stylesheets/framework/sidebar.scss

@@ -20,10 +20,6 @@
     transition-duration: .3s;
   }
-  .hide-sidebar{
-    overflow: hidden !important;
-  }
-
   .gitlab-text-container-link {
     z-index: 1;
     position: absolute;