How to make a drop down list (sub-sub ul)?

Question

css

Hello.
I got into a stupor .. not much to understand what is wrong with me.
There is such a structure of the drop-down list of the horizontal menu:

<nav class="mnav_class">
    <ul id="m_id" class="m_class">
        <li id="" class=""><a href="" aria-current="page">Главная</a></li>
        <li id="" class=""><a title="" href="">Стр_1</a>
            <ul class="sub-menu">
                <li id="" class=""><a href="">Подстр_1.1</a>
                    <ul class="sub-menu">
                        <li id="" class=""><a href="">Подстр_1.1.1</a></li>
                        <li id="" class=""><a href="">Подстр_1.1.2</a></li>
                    </ul>
                </li>
                <li id="" class=""><a title="" href="">Подстр_2</a>
                    <ul class="sub-menu">
                        <li id="" class=""><a href="">Под стр_2.1</a></li>
                        <li id="" class=""><a href="">Под стр_2.2</a></li>
                    </ul>
                </li>
            </ul>
        </li>
    </ul>
</nav>

I’m stupid, but I can’t figure out how to make the sub-menu (the first nested list) open after hovering over li, and the second nested list would not open, but would open after hovering over the sub-menu li (the second nested list).

Answer 1

li:hover > . sub-menu