CLASSROOMIO-T-41: Implement dark/light mode switch

Co-authored-by: Rotimi Best <rotimiibitoyeemma@gmail.com>

Merge-request: CLASSROOMIO-MR-8
Merged-by: Digdippa Team <digdippa@gmail.com>

src/components/PageBody/index.svelte

@@ -9,7 +9,7 @@
 <div class="root mt-4 mx-auto {width} {className} relative {padding}">
   {#if $$slots.header}
     <div
-      class="head flex items-center justify-between sticky right-0 w-full px-3"
+      class="head dark:bg-gray-800 flex items-center justify-between sticky right-0 w-full px-3"
     >
       <slot name="header" />
     </div>
@@ -26,6 +26,5 @@
   .head {
     top: 0px;
     z-index: 1;
-    background-color: #fafbfc;
   }
 </style>