Use btn-dark everywhere. Closes BiscuIT-ng#94.

biscuit/apps/alsijil/templates/alsijil/group_week.html

@@ -11,12 +11,12 @@
       <ul id="timetable_select_form">
         {{ select_form.as_ul }}
       </ul>
-      <button type="submit" class="btn btn-secondary">
+      <button type="submit" class="btn btn-dark">
         {% blocktrans %}Select{% endblocktrans %}
       </button>
     </form>
     {% if group %}
-      <a class="btn btn-secondary" href="{% url 'full_register_group' group.id %}">
+      <a class="btn btn-dark" href="{% url 'full_register_group' group.id %}">
         {% fa 'print' %}
       </a>
     {% endif %}