[Blazor][Fixes #22895] Page header can be covered by other elements when there...

[Blazor][Fixes #22895] Page header can be covered by other elements when there is a lot of content on the page (#24005)

Adds z-index to top-row to avoid the header being covered by other elements

src/Components/Samples/BlazorServerApp/wwwroot/css/site.css

@@ -24,6 +24,7 @@ app {
     height: 3.5rem;
     display: flex;
     align-items: center;
+    z-index: 10;
 }
 
 .main {

src/ProjectTemplates/Web.ProjectTemplates/content/BlazorServerWeb-CSharp/wwwroot/css/site.css

@@ -24,6 +24,7 @@ app {
     height: 3.5rem;
     display: flex;
     align-items: center;
+    z-index: 10;
 }
 
 .main {

src/ProjectTemplates/Web.ProjectTemplates/content/ComponentsWebAssembly-CSharp/Client/wwwroot/css/app.css

@@ -24,6 +24,7 @@ app {
     height: 3.5rem;
     display: flex;
     align-items: center;
+    z-index: 10;
 }
 
 .main {