Fix the width available to page content (#5299)

Signed-off-by: Miki <miki@amazon.com>

_sass/_nested-nav.scss

@@ -69,6 +69,13 @@
         }
       }
 
+      &:last-child {
+        > ul {
+          right: .5em;
+          left: auto;
+        }
+      }
+
       &:hover {
         > ul {
           display: block;

_sass/custom/custom.scss

@@ -286,7 +286,8 @@ img {
   position: fixed;
   bottom: 30px;
   right: 16px;
-  z-index: 1;
+  z-index: 999;
+
   svg {
     transform: rotate(-90deg);
   }
@@ -515,6 +516,10 @@ p.label {
 // Adds TOC to right hand side in xl layout
 .main-content-wrap {
   width: 100%;
+
+  @include mq(xl) {
+    width: calc(100% - #{$toc-width});
+  }
 }
 
 .toc-wrap {