fix(sidenav): unable to scroll sidenav as expected (angular#978)

- fixes a bug in sidenav where user has to scroll to bottom
  of the page to reach bottom of navigation

Fixes angular#857

Co-authored-by: Michael Prentice <[email protected]>

Author: jljohnson001

material.angular.io/src/app/pages/component-sidenav/component-sidenav.scss

@@ -33,7 +33,7 @@ app-component-sidenav {
 
   .docs-component-viewer-nav-content {
     width: constants.$sidenav-width;
-    height: 100vh;
+    height: calc(100vh - 56px);
     overflow: auto;
 
     &::-webkit-scrollbar {