Add focus-visible polyfill, issue #187 (#193)

* add focus-visible polyfill
* remove unnecessary outline: none from styles
* make buttons Pin, Block, Delete visible when focused
* fix outline of user details close button
* close user info by ESC
* user info: don't focus the close button

web/app/components/comment/__action/comment__action.scss

@@ -9,10 +9,6 @@
     color: #31c7c5;
   }
 
-  &:focus {
-    outline: none;
-  }
-
   + .comment__action {
     margin-left: 8px;
   }

web/app/components/comment/__control/comment__control.scss

@@ -10,8 +10,4 @@
   &:hover {
     color: #0aa;
   }
-
-  &:focus {
-    outline: none;
-  }
 }

web/app/components/comment/__controls/comment__controls.scss

@@ -4,9 +4,10 @@
   user-select: none;
   font-size: 14px;
   font-weight: 700;
+  opacity: 0;
 
-  @media (hover: hover) {
-    font-weight: 700;
-    opacity: 0;
+  &:hover,
+  &:focus-within {
+    opacity: 1;
   }
 }

web/app/components/comment/__vote/comment__vote.scss

@@ -8,7 +8,6 @@
   background: url('comment__vote.svg') center no-repeat;
   background-size: contain;
   cursor: pointer;
-  outline: none;
 
   &:hover {
     background-image: url('_selected/comment__vote_selected.svg');