filled some styling lacunae, including structural fixes to html re: gatekeeper gear menu

src/templates/apps/gameboard/_partials/_gatekeeper.html

@@ -74,7 +74,7 @@
             {% if request.user == room.owner %}
                 <form method="POST" action="{% url 'epic:invite_gamer' room.id %}">
                     {% csrf_token %}
-                    <input type="email" name="invitee_email" id="id_invite_email" placeholder="friend@example.com">
+                    <input type="email" name="invitee_email" id="id_invite_email" class="form-control form-control-lg" placeholder="friend@example.com">
                     <button type="submit" id="id_invite_btn" class="btn btn-primary btn-xl">Invite</button>
                 </form>
             {% endif %}