bg-card will be added to the class and password/username validation

bg-card should not be an id, ids should be unique in their use.

src/main/resources/templates/misc/adjust-contrast.html

@@ -20,7 +20,7 @@
         <br><br>
         <div class="container">
           <div class="row justify-content-center">
-            <div class="col-md-12" id="bg-card">
+            <div class="col-md-12 bg-card">
               <div class="row justify-content-center">
                 <div class="col-md-3">
                   <div id="sliders-container" style="display:none;">