I am working on a small website for my teacher and I am supposed to do a navigation menu with submenu (I am using :hover). That website will be used on computer and on tablets or Ipad. My menu is finished but on tablets I encounter the following issue : my submenu shows well but it does not hide when I touch elsewhere on the screen (except on the logo - do not know why). An other student told me he found a solution but when he touched one of the links in the submenu, the submenu hide and this is not the result I want. Our teacher told us we must absolutely not use something else than HTML and CSS (No JS, no Jquery).
Here is my code :
body > header > nav {
    min-width: 768px;
    margin: 0 auto;
    padding-top: 20px;
    font-size: 1.5em;
    text-align: center;
}
nav > ul ul {
    position: absolute;
    left: -999em;
    text-align: left;
}
nav li {
    width: 150px;
}
nav > ul > li {
    display: inline-block;
}
nav a {
    display: block;
    text-decoration: none;
}
nav > ul > li > a {
    padding: 10px 0;
    color: #44546A;
}
nav > ul ul li {
    background-color: #333F50;
    list-style-type: none;
}
nav > ul ul li a {
    padding: 10px 0 10px 30px;
}
nav > ul ul li a {
    color: #FAFAFA;
    font-size: 0.9em;
}
nav > ul ul li:hover {
    background-color: #51647f;
}
nav > ul li:hover ul {
    left: auto;
}<html>    
    <body>
         <header>
            <img src="img/logo_def_vect.svg" alt="Logo"/>
            <nav>
                <ul>
                    <li>
                        <a href="#">Menu1</a>
                        <ul>
                            <li>
                                <a href="#">SubMenu1.1</a>
                            </li>
                        </ul>
                    </li>
                    <li><a href="#">Menu2</a>
                        <ul>
                            <li>
                                <a href="#">SubMenu2.2</a>
                            </li>
                            <li>
                                <a href="#">SubMenu2.3</a>
                            </li>
                        </ul>
                    </li>
                </ul>
            </nav>
        </header>
    </body>
</html> 
    