SPR-908: all z-indices are found in base_structure.less,

SPR-908: Bugfix Direct-nav in Tableview should be above toggle button

css/area_main-sidebar-nav.less

@@ -119,7 +119,6 @@
             &:focus,
             &:active {
                 position: relative; // always show label, even with collapsed sidebar
-                z-index: 100; // show label/link above content on hover etc.
                 width: 100%;
                 background-color: @ini_nav_menu_hover_bg;
                 border-color: @ini_nav_menu_hover_color;
@@ -316,7 +315,6 @@
             display: block !important;
             position: absolute;
             left: 1.25rem; // left margin of content container
-            z-index: 200; // mobile sidebar above all
             box-shadow: @box-shadow-right-bottom;
             min-width: 45%;
             max-width: 90%;