Update dark.css to improve visibility (#13749)

Fixed certain colours to make them more readable against the dark background. Mainly the blue colour against the dark background I have changed to a lighter blue.
Some dark greys and blacks as well.

html/css/dark.css

@@ -7236,3 +7236,26 @@
     background: #3e444c;
     text-align: center;
   }
+
+  .interface-upup,
+  a.interface-upup {
+    color: #1c86e1;
+  }
+
+  A.blue:visited, A.blue, .blue    { color: #008cff;}
+
+  A.grey:visited, A.grey, .grey    { color: #8c99ad;}
+
+  A.red:visited, A.red, .red    { color: d61818;}
+
+  .select2-container--default .select2-selection--multiple .select2-selection__choice {
+    background-color: #32373d;
+  }
+
+  .select2-container--default .select2-results__option[aria-selected=true] {
+    background-color: #2d3238;
+  }
+
+  .select2-container--default .select2-results__option[aria-selected=false] {
+    background-color: #3E444C;
+  }