Smopp_v2/loco.php

<div class="container border-box mt-1">
    <div class="content__main__form__item">
        <p class="content__main__form__text">
            Серия локомотива
        </p>
        <div class="content__main__form__inputs">
            <select id="series" style="width: 600px;" class="form-input content__main__form__series" name="loco_type">
                <option value="0">
                    &lt;Выберите серию локомотива&gt;
                </option>
            </select>
        </div>
    </div>

    <div id="sections_container" class="content__main__form__item" style="display:none">
        <p id="chosenserie" class="content__main__form__text"></p>
        <div class="content__main__form__inputs">
            <select id="sections" style="width: 600px;" class="form-input content__main__form__series" name="sections">
                <option value="0">
                    &lt;Выберите секцию&gt;
                </option>
            </select>
        </div>
        <br>
        <input id="add_new_section" type="button" value="">
    </div>

    <div id="add_section_container" class="content__main__form__item" style="display:none">
        <p class="content__main__form__text">Добавьте данные новой секции</p>
        Номер <input min="1" id="number" type="number" value="number">
        Субномер <input min="8" id="subnumber" type="number" value="subnumber">
        <select id="section_letter" style="width: 600px;" name="section_letter">
            <option value="А">А</option>
            <option value="Б">Б</option>
            <option value="В">В</option>
            <option value="Г">Г</option>
        </select><br>
        <input id="write_section" type="button" value="Добавить">
    </div>

    <div id="section_container" class="content__main__form__item" style="display:none">
        <p class="content__main__form__text">Информация по выбранной секции</p>
        <div id="section_content">
        </div>
        <input id="delete_section" type="button" value="Удалить секцию из базы">
    </div>

    <div id="sections_load" class="content__main__form__item" style="display:none">
        <input id="getsectionlist" type="button" value="Загрузить секции АСУ СГ">
    </div>
    <div id="result"></div>
</div>
<style type="text/css">
    .container {
        margin-top: 10px;
        max-width: 550px;
    }
    .content__main__form__item {
        width: 100%;
    }
    input[type="button"] {
        display: block;
        margin: 0 auto;
    }
</style>