non va :C

<body>

    <div id="top-bar">
        <a href="https://www.kyrosdesign.net">KYROSDESIGN.net</a>
    </div>
    <div class="buttons">
        <div class="left"></div>
        <div class="right"></div>
    </div>
    <nav>
        <div class="title">Admin Panel</div>
        <ul>
            <li id="home" class="active">Home</li>
            <li id="analytics">Analytics</li>
            <li id="newpost">New Post</li>
            <li id="messages">Messages</li>
            <li id="products">Products</li>
        </ul>
    </nav>

    <div class="content">
        <div class="act-container">

            <div id="home-act" class="act activeAct">
            </div>
            <div id="analytics-act" class="act">
            </div>
            <div id="newpost-act" class="act">
            </div>
            <div id="messages-act" class="act">
            </div>
            <div id="products-act" class="act">
            </div>

        </div>
    </div>

</body>

<script>
let homeAct = document.getElementById('home-act');
let analyticsAct = document.getElementById('analytics-act');
let newpostAct = document.getElementById('newpost-act');
let messagesAct = document.getElementById('messages-act');
let productsAct = document.getElementById('products-act');

let home = document.getElementById('home');
let analytics = document.getElementById('analytics');
let newpost = document.getElementById('newpost');
let messages = document.getElementById('messages');
let products = document.getElementById('products');

$('li').click(function () {
    $('li').removeClass('active');
    $(this).addClass('active');
});

if (home.classList.contains('active')) {
    homeAct.classList.add('activeAct');
} else {
    homeAct.classList.remove('activeAct');
}

if (analytics.classList.contains('active')) {
    analyticsAct.classList.add('activeAct');
} else {
    analyticsAct.classList.remove('activeAct');
}

if (newpost.classListclassList.contains('active')) {
    newpostAct.classList.add('activeAct');
} else {
    newpostAct.classList.remove('activeAct');
}

if (messages.classList.contains('active')) {
    messagesAct.classList.add('activeAct');
} else {
    messagesAct.classList.remove('activeAct')
}

if (products.classList.contains('active')) {
    productsAct.classList.add('activeAct');
} else {
    productsAct.classList.remove('activeAct')
}
</script>