Contact Form 7 で bootstrap3を使う

form にclassを追加する
ショートコードに追加

[contact-form-7 id="120" title="フォーム" html_class="form-horizontal"]

<div class="panel panel-default">
    <div class="panel-heading">
        <h2 class="panel-title"><i class="fa fa-file-text-o"></i>フォーム</h2>
    </div>
    <div class="form-group">
        <label class="col-sm-2 control-label">お名前</label>
        <div class="col-sm-8">
            [text* your-name class:form-control]
        </div>
    </div>
    <div class="form-group">
        <label class="col-sm-2 control-label">ふりがな</label>
        <div class="col-sm-8">
            [text* your-hurigana class:form-control]
        </div>
    </div>
    <div class="form-group">
        <label class="col-sm-2 control-label">メールアドレス</label>
        <div class="col-sm-8">
            [email* your-email class:form-control] </p>
        </div>
    </div>
    <div class="form-group">
        <label class="col-sm-2 control-label">性別</label>
        <div class="col-sm-8">[checkbox* your-sex class:form-control use_label_element exclusive "男性" "女性"]</div>
    </div>
    <div class="form-group">
        <label class="col-sm-2 control-label">生年月日</label>
        <div class="col-sm-8">[text* your-birthday class:form-control] </div>
    </div>
    <div class="form-group">
        <label class="col-sm-2 control-label">住所</label>
        <div class="col-sm-8">[text* your-add class:form-control] </div>
    </div>
    <div class="form-group">
        <label class="col-sm-2 control-label">電話番号</label>
        <div class="col-sm-8">[text* your-tel class:form-control] </div>
    </div>

    <div class="form-group">
        <label class="col-sm-2 control-label">結婚</label>
        <div class="col-sm-8">[select* your-marriage class:form-control "既婚" "未婚"] </div>
    </div>
    <div class="form-group">
        <div class="col-sm-offset-2 col-sm-10">[submit class:btn class:btn-default "送信"]</div>
    </div>
    </div>
</div>

複数classを指定したい場合は並べる。
submit で利用可能なオプション