Remove body scrollbar in chat layout, keep nav bar still on scroll lock, add tiny fade for media modal

src/App.scss

@@ -586,6 +586,7 @@ nav {
   color: var(--faint, $fallback--faint);
   box-shadow: 0px 0px 4px rgba(0,0,0,.6);
   box-shadow: var(--topBarShadow);
+  box-sizing: border-box;
 }
 
 .fade-enter-active, .fade-leave-active {
@@ -878,6 +879,11 @@ nav {
   overflow: hidden;
   height: 100%;
 
+  // Get rid of scrollbar on body as scrolling happens on different element
+  body {
+    overflow: hidden;
+  }
+
   // Ensures the fixed position of the mobile browser bars on scroll up / down events.
   // Prevents the mobile browser bars from overlapping or hiding the message posting form.
   @media all and (max-width: 800px) {

src/components/media_modal/media_modal.vue

@@ -73,11 +73,22 @@
   }
 }
 
+@keyframes media-fadein {
+  from {
+    opacity: 0;
+  }
+  to {
+    opacity: 1;
+  }
+}
+
 .modal-image {
   max-width: 90%;
   max-height: 90%;
   box-shadow: 0px 5px 15px 0 rgba(0, 0, 0, 0.5);
   image-orientation: from-image; // NOTE: only FF supports this
+  opacity: 1;
+  animation: 0.1s cubic-bezier(0.7, 0, 1, 0.6) media-fadein;
 }
 
 .modal-view-button-arrow {