Add z-index

app/assets/stylesheets/content/editor/_ckeditor.sass

@@ -84,6 +84,7 @@
   .document-editor__toolbar
     position: sticky
     top: 0
+    z-index: 1
 
   .ck.ck-toolbar.ck-rounded-corners
     border-bottom-left-radius: 0
@@ -97,14 +98,9 @@
     border-top-right-radius: 0
 
   .ck-editor__editable
-
-    /* Keep the "page" off the boundaries of the container. */
     padding: 1cm 2cm 2cm
-
     border: 1px hsl( 0,0%,82.7% ) solid
     border-radius: var(--ck-border-radius)
     background: white
-
-    /* The "page" should cast a slight shadow (3D illusion). */
     box-shadow: 0 0 5px hsla( 0,0%,0%,.1 )