fix(version dropdown): z-index fix for version dropdown and header (#3190)

Author: EvilAlexei

demo/src/app/common/top-menu/top-menu.component.html

@@ -10,7 +10,7 @@ <h1 class="logo" >
       <div dropdownToggle class="dropdown-toggle">
         {{currentVersion ? 'v' + currentVersion : ''}} <span class="caret"></span>
       </div>
-      <ul *dropdownMenu class="dropdown-menu" role="menu">
+      <ul *dropdownMenu class="dropdown-menu header-dropdown" role="menu">
         <li role="menuitem" *ngFor="let item of previousDocs">
           <a class="dropdown-item" [href]="appUrl + (needPrefix ? item.url : item.unprefixedUrl) + (appHash ? '/' + appHash : '')">{{item.version}}</a>
         </li>

demo/src/assets/css/style.scss

@@ -509,6 +509,9 @@ a:hover {
     top: 0;
     z-index: 1090; // to overlap most positioned elements in bootstrap
   }
+  .header-dropdown {
+    z-index: 1090;
+  }
   .modal-backdrop {
     z-index: 2000; // to overlap header :)
   }