Restructure button nav bar on lesson overview page

aleksis/apps/alsijil/templates/alsijil/class_register/lesson.html

@@ -56,17 +56,20 @@
         {# Back to week view #}
         {% if back_to_week_url %}
           <a href="{{ back_to_week_url }}"
-             class="btn primary-color waves-light waves-effect margin-bottom hide-on-small-only">
-            <i class="material-icons left">chevron_left</i> {% trans "Week view" %}
-          </a>
-          <a href="{{ back_to_week_url }}"
-             class="btn primary-color waves-light waves-effect hundred-percent margin-bottom hide-on-med-and-up">
+             class="btn secondary-color waves-light waves-effect margin-bottom {% if prev_lesson_person or next_lesson_person %}hide-on-extra-large-only{% endif %}">
             <i class="material-icons left">chevron_left</i> {% trans "Week view" %}
           </a>
         {% endif %}
 
         {% if prev_lesson_person or next_lesson_person %}
           <div class="col s12 no-padding center alsijil-nav">
+            {% if back_to_week_url %}
+              <a href="{{ back_to_week_url }}"
+                 class="btn-flat secondary-color-text waves-light waves-effect left hide-on-med-and-down hide-on-large-only show-on-extra-large">
+                <i class="material-icons left">chevron_left</i> {% trans "Week view" %}
+              </a>
+            {% endif %}
+
             {# Previous lesson #}
             <a class="btn-flat waves-effect waves-light left primary-color-text {% if not prev_lesson_person %}disabled{% endif %}"
                title="{% trans "My previous lesson" %}"