Dark mode + Demo component - CSS Class updated

Author: gvreddy04

BlazorBootstrap.Demo.RCL/Components/Shared/Demo.razor

@@ -73,7 +73,7 @@ else // Tabs = true
                         <Icon Name="@clipboardTooltipIconName" Color="@clipboardTooltipIconColor" />
                     </Tooltip>
                 </div>
-                <div class="highlight">
+                <div class="highlight border border-top-0">
                     <pre class="mt-0 me-4">
                         <code class="@LanguageCode.ToLanguageCssClass()">
                             @if (snippet is not null)