Use stickybits on sidenav

styles/components/_topbar.scss

@@ -1,11 +1,11 @@
 .topbar {
   background-color: $color-blue-darkest;
   border-bottom: 1px solid $color-black;
-  z-index: 16;
   height: 48px;
 
   &.js-is-sticky {
     width: 100%;
+    z-index: 16;
   }
 
   &__navigation {

styles/elements/_sidenav.scss

@@ -4,20 +4,20 @@
 }
 
 .sidenav-container {
-  position: relative;
   box-shadow: $box-shadow;
-  width: 19.2%;
-  min-width: 25rem;
-
-  .global-navigation.sidenav {
-    height: 100%;
-  }
 
   .sidenav {
     @include media($large-screen) {
       margin: 0px;
     }
 
+    width: 25rem;
+
+    &.js-is-sticky {
+      width: 19.2%;
+      min-width: 25rem;
+    }
+
     &__title {
       @include sidenav__header;
 
@@ -184,5 +184,9 @@
 
     width: 10rem;
     margin: 0px;
+
+    &.js-is-sticky {
+      width: 10rem;
+    }
   }
 }