Improve poll link accessibility (#10720)

* Add distinction between hover and active/focus states
* Resolves #10198

app/javascript/styles/mastodon/polls.scss

@@ -114,11 +114,14 @@
     text-decoration: underline;
     font-size: inherit;
 
-    &:hover,
-    &:focus,
-    &:active {
+    &:hover {
       text-decoration: none;
     }
+
+    &:active,
+    &:focus {
+      background-color: rgba($dark-text-color, .1);
+    }
   }
 
   .button {