fix z-index

assets/sass/_theme/configuration/spacings.sass

@@ -25,7 +25,8 @@ $zindex-nav-accessibility: 1010 !default
 $zindex-stretched-link: 2 !default
 $zindex-header: 52 !default
 $zindex-body-overlay: 51 !default
-$zindex-toc: 60 !default
+$zindex-toc-offcanvas: 60 !default
+$zindex-toc: 50 !default
 $zindex-toc-cta: 49 !default
 $zindex-modal: 72 !default
 $zindex-aside: 48 !default

assets/sass/_theme/design-system/table_of_contents.sass

@@ -6,7 +6,7 @@
     right: 0
     bottom: 0
     margin-top: 0
-    z-index: $zindex-toc
+    z-index: $zindex-toc-offcanvas
     width: calc(#{columns(4)} + var(--grid-gutter) * 2)
     transform: translateX(100%)
     transition: var(--toc-transition-duration) transform ease-in-out
@@ -131,6 +131,7 @@
         height: 100%
         position: absolute
         width: columns(4)
+        z-index: $zindex-toc
         .toc-content
             overflow-y: auto
             max-height: calc(100vh - var(--header-height))