{% macro render_submit() %}
<div class="control-group">
  <div class="controls">
    <input class="btn btn-secondary mb-4" type="submit"
    {%- for key, value in kwargs.items() %}
      {{key}}="{{value}}"
    {% endfor %}
    />
  </div>
</div>
{%- endmacro %}

{% macro render_field(field) %}
  {% if field.type in ['HiddenField', 'CSRFTokenField'] %}
    {{ field()|safe }}
  {% else %}
<div class="control-group">
  <label class="form-label">{{ field.label }}</label>
  <div class="controls">
    {{ field(class_="form-control mb-4", **kwargs)|safe }}
    {{ render_errors(field.errors) }}
  </div>
</div>
{% endif %}
{%- endmacro %}

{% macro render_errors(errors) %}
  {%- if errors|length == 1 %}
  <div class="errors">
    {{ errors.0 }}
  </div>
  {% elif errors %}
  <ul class="errors">
  {% for error in errors %}
    <li>{{ error }}</li>
  {% endfor %}
  </ul>
  {% endif %}
{%- endmacro %}