message: fix(docs-infra): make hamburger menu non focusable when not visible
  the header hamburger menu gets removed from the page by moving it
  outside the screen, it can however still be accessed via keyboard
  navigation, add a visibility hidden to the element to prevent such
  behavior
  PR Close
diff: @@ -34,6 +34,7 @@ mat-toolbar.app-toolbar {
  .hamburger {
  // Hamburger shown on non-marketing pages even on large screens.
  margin: $hamburgerShownMargin;
  + visibility: visible;
  }
  }
  }
  @@ -52,6 +53,7 @@ mat-toolbar.app-toolbar {
  // Hamburger hidden by default on large screens.
  // (Will be shown per doc.)
  margin: $hamburgerHiddenMargin;
  + visibility: hidden;
  }
  @media (max-width: 480px) {
  