More contrasting focus ring in Dark Mode

Fixes #279

Author: philwareham

src/assets/sass/setup/_colours.scss

@@ -37,7 +37,7 @@ $color-selected:                      tint($color-link-hover, 90%) !default;
 
 $dark-color-link:                     #9cd7ff !default;
 $dark-color-link-hover:               tint($dark-color-link, 33%) !default;
-$dark-color-link-focus:               darken(#ffda44, 15%) !default;
+$dark-color-link-focus:               #ff00cc !default;
 $dark-color-selecting:                #1b2f48 !default;
 $dark-color-selected:                 #1c3456 !default;