Hide some components rather than unmounting (#2271)

Hide some components rather than unmounting them to allow to show again
quickly and keep the view state such as the scrolled offset.

app/assets/stylesheets/containers.scss

@@ -9,6 +9,16 @@
   }
 }
 
+.mastodon-column-container {
+  display: flex;
+  height: 100%;
+  width: 100%;
+
+  // 707568 - height 100% doesn't work on child of a flex item - chromium - Monorail
+  // https://bugs.chromium.org/p/chromium/issues/detail?id=707568
+  flex: 1 1 auto;
+}
+
 .logo-container {
   max-width: 400px;
   margin: 100px auto;
@@ -40,7 +50,7 @@
 
       img {
         opacity: 0.8;
-        transition: all 0.8s ease;
+        transition: opacity 0.8s ease;
       }
 
       &:hover {