Style language dropdown in theme colours.

biscuit/core/templates/core/language_form.html

@@ -3,7 +3,7 @@
 <form action="{% url 'set_language' %}" method="post">
   {% csrf_token %}
   <input name="next" type="hidden" value="{{ request.get_full_path }}">
-  <select name="language" onchange="this.form.submit()">
+  <select name="language" onchange="this.form.submit()" class="form-control bg-light text-dark border-2 border-dark">
     {% get_current_language as LANGUAGE_CODE %}
     {% get_available_languages as LANGUAGES %}
     {% get_language_info_list for LANGUAGES as languages %}