fix($core): add missing styles for OutboundLink (#2662)

Author: Mister-Hope

packages/@vuepress/core/lib/client/components/OutboundLink.vue

@@ -43,3 +43,16 @@ export default {
   top: -1px;
 }
 </style>
+
+<style lang="stylus">
+.sr-only
+  position absolute
+  width 1px
+  height 1px
+  padding 0
+  margin -1px
+  overflow hidden
+  clip rect(0, 0, 0, 0)
+  white-space nowrap
+  border-width 0
+</style>

packages/@vuepress/theme-default/styles/index.styl

@@ -189,17 +189,6 @@ th, td
     .sidebar
       top 0
 
-.sr-only 
-  position absolute
-  width 1px
-  height 1px
-  padding 0
-  margin -1px
-  overflow hidden
-  clip rect(0, 0, 0, 0)
-  white-space nowrap
-  border-width 0
-
 @media (min-width: ($MQMobile + 1px))
   .theme-container.no-sidebar
     .sidebar