webapp/templates/default/module/room.html.twig

<form name="room" action="{{ path('room_add') }}" method="post">
    {% if request.get('error') %}
        <output name="error" for="form-room-name">{{ request.get('error') }}</output>
    {% endif %}
    {% if request.get('warning') %}
        <output name="warning" for="form-room-name">{{ request.get('warning') }}</output>
    {% endif %}
    <input type="text" name="name" id="form-room-name" value="{{ request.get('name') }}" placeholder="{{ 'enter new room name...' | trans }}" />
    <button type="submit">{{ 'add' | trans }}</button>
    {% if cost %}
        <span>{{ 'cost: %s KVA' | format(cost) | trans }}</span>
    {% endif %}
    <input type="hidden" name="token" value="{{ token }}" />
</form>