Dashboard updates (#26179)

* Update Dashboard example

- Replaces .sticky-top on .navbar with .fixed-top
- Adjusts padding on main content area and sidebar to account for fixed navbar
- Move to padding in sidebar instead of top: 48px; fixes Firefox rendering issue
- Adds new .shadow utility for a little extra cherry on top
- Moves sticky styles to separate feature query ruleset to avoid IE rendering issues

* Add .w-100 to chart to fix IE horizontal scroll from label that extended past viewport

docs/4.0/examples/dashboard/dashboard.css

@@ -18,20 +18,26 @@ body {
   bottom: 0;
   left: 0;
   z-index: 100; /* Behind the navbar */
-  padding: 0;
+  padding: 48px 0 0; /* Height of navbar */
   box-shadow: inset -1px 0 0 rgba(0, 0, 0, .1);
 }
 
 .sidebar-sticky {
-  position: -webkit-sticky;
-  position: sticky;
-  top: 48px; /* Height of navbar */
+  position: relative;
+  top: 0;
   height: calc(100vh - 48px);
   padding-top: .5rem;
   overflow-x: hidden;
   overflow-y: auto; /* Scrollable contents if viewport is shorter than content. */
 }
 
+@supports ((position: -webkit-sticky) or (position: sticky)) {
+  .sidebar-sticky {
+    position: -webkit-sticky;
+    position: sticky;
+  }
+}
+
 .sidebar .nav-link {
   font-weight: 500;
   color: #333;
@@ -56,6 +62,14 @@ body {
   text-transform: uppercase;
 }
 
+/*
+ * Content
+ */
+
+[role="main"] {
+  padding-top: 48px; /* Space for fixed navbar */
+}
+
 /*
  * Navbar
  */