Fade in animation for card (#3521)

* fade in and out the card

one more fix

dont leave an invisible card behind

okay just about there

move styles

glitch

clear hide timeouts on card enter

about there

* Tweak timings

* Rewrite with explicit states

---------

Co-authored-by: Dan Abramov <dan.abramov@gmail.com>

web/index.html

@@ -239,6 +239,16 @@
         inset:0;
         animation: rotate 500ms linear infinite;
       }
+
+      @keyframes avatarHoverFadeIn {
+        from { opacity: 0; }
+        to { opacity: 1; }
+      }
+
+      @keyframes avatarHoverFadeOut {
+        from { opacity: 1; }
+        to { opacity: 0; }
+      }
     </style>
   </head>