Make the element picker dialog slowly fade away when made discrete

This fixes the following issues:
- #3449
- uBlockOrigin/uBlock-issues#55

src/epicker.html

@@ -180,10 +180,24 @@
     width: calc(40% - 4px) !important;
 }
 #ublock0-epicker body.paused > aside {
-    opacity: 0.1 !important;
+    opacity: 0.1;
     visibility: visible !important;
     z-index: 100 !important;
 }
+/**
+    https://github.com/gorhill/uBlock/issues/3449
+    https://github.com/uBlockOrigin/uBlock-issues/issues/55
+**/
+@keyframes startDialog {
+  0% { opacity: 1.0; }
+  60% { opacity: 1.0; }
+  100% { opacity: 0.1; }
+}
+#ublock0-epicker body.paused > aside:not(:hover):not(.show) {
+    animation-duration: 1.6s !important;
+    animation-name: startDialog !important;
+    animation-timing-function: linear !important;
+}
 #ublock0-epicker body.paused > aside:hover {
     opacity: 1 !important;
 }