refactor(Sidebar): update z-index

Author: mrholek

scss/_variables.scss

@@ -1185,9 +1185,10 @@ $form-validation-states: (
 $zindex-dropdown:                   1000 !default;
 $zindex-sticky:                     1020 !default;
 $zindex-fixed:                      1030 !default;
-$zindex-sidebar-backdrop:           1030 !default;
 $zindex-offcanvas-backdrop:         1040 !default;
+$zindex-sidebar-backdrop:           1040 !default;
 $zindex-offcanvas:                  1045 !default;
+$zindex-sidebar-overlaid:           1045 !default;
 $zindex-modal-backdrop:             1050 !default;
 $zindex-modal:                      1055 !default;
 $zindex-popover:                    1070 !default;

scss/sidebar/_sidebar.scss

@@ -9,6 +9,7 @@
   --#{$prefix}sidebar-color: #{$sidebar-color};
   --#{$prefix}sidebar-brand-color: #{$sidebar-brand-color};
   --#{$prefix}sidebar-brand-bg: #{$sidebar-brand-bg};
+  --#{$prefix}sidebar-overlaid-zindex: #{$zindex-sidebar-overlaid};
   // scss-docs-end sidebar-css-vars
 
   position: relative;
@@ -79,7 +80,6 @@
       position: fixed;
       top: 0;
       bottom: 0;
-      z-index: $zindex-fixed;
 
       &:not(.sidebar-end) {
         @include ltr-rtl("left", 0);
@@ -103,7 +103,7 @@
     position: fixed;
     top: 0;
     bottom: 0;
-    z-index: $zindex-fixed + 2;
+    z-index: var(--#{$prefix}sidebar-overlaid-zindex);
 
     &:not(.hide) {
       box-shadow: $box-shadow;
@@ -130,7 +130,7 @@
     position: fixed;
     top: 0;
     bottom: 0;
-    z-index: $zindex-fixed + 1;
+    z-index: var(--#{$prefix}sidebar-overlaid-zindex);
 
     &:not(.sidebar-end) {
       @include ltr-rtl("left", 0);