maple-bbs/templates/search/form.html

<form class="form-inline text-center" action="{{ url_for('search.search') }}">
  <div class="input-group">
    <div class="input-group-addon">关键字:</div>
    <input type="text" class="form-control" name="keyword" placeholder="搜索关键字">
    <div class="input-group-addon" style="padding:0px;border:none;width:145px;">
      <select name="include" class="form-control" style="border-left-style:none;">
        <option value="0">包含标题和内容</option>
        <option value="1">仅搜索标题</option>
        <option value="2">仅搜索内容</option>
      </select>
    </div>
  </div>
  <button type="submit" class="btn btn-primary" style="width:120px;">搜索</button>
</form>