style(next): icon buttons: add a style for the visible focus state

src/public/stylesheets/theme-next/forms.css

@@ -105,6 +105,10 @@ button.btn.btn-success kbd {
     transform: scale(.85);
 }
 
+:root .icon-action:not(.global-menu-button):focus-visible {
+    outline: 2px solid var(--input-focus-outline-color);
+}
+
 /* 
  * Input boxes
  */