Why is my item taking up space when display is none?

I am making a dropdown navigation menu and one of the list items takes up space when I set display to none. The 'Book A Table' item isn't supposed to be displayed in the centre div when above 1100px then should be displayed in the dropdown menu when below 1100px. I used the inspect element on chrome and there's a green line where the item is still there.

<!DOCTYPE html>
<html lang="en">

    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Dropdown Menu</title>
        <link href="styles.css" rel="stylesheet">
        <link href='https://unpkg.com/[email protected]/css/boxicons.min.css' rel='stylesheet'>
    </head>

    <body>
        
        <header class="header">

            <div class="toggle-button" onclick="myFunction();">
                <span class="bar1"></span>
                <span class="bar2"></span>
                <span class="bar3"></span>   
            </div>

            <div class="logo">
                <a href="index.html"><img src="darklogo.png" alt=""></a>
            </div>


            <nav id="nav">
                <ul>
                    <li><a href="#">Home</a></li>
                    <li><a href="#">Menu</a></li>
                    <li><a href="#">About Us</a></li>
                    <li><a href="#">Contact Us</a></li>
                    <li><a href="#" class="bookatabledd">Book A Table</a></li>
                </ul>
            </nav>

            <div class="bookatable">Book A Table &nbsp ></div>


        </header>

        <script src="main.js"></script>

    </body>

</html>

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: Arial, Helvetica, sans-serif;
}


header {
    display: flex;
    text-align: center;
    justify-content: space-between;
    align-items: center;
    width: 100%;
    padding: 5px 60px;
    background-color: #212223;
    position: relative;
}


.logo img {
    width: 190px;
}

.bookatabledd {
    display: none;
}

nav ul li {
    display: inline-block;
    padding: 5px 25px;
}

nav ul li a{
    display: inline-block;
    font-weight: bold;
    font-size: 20px;
    list-style-type: none;
}

nav ul li a:hover {
    color: rgb(174, 17, 174);
}

nav ul li a{
    text-decoration: none;
    display: inline-block;
    color: white;
    font-weight: 600;
}


.toggle-button{
    width: 35px;
    position: absolute;
    right: 40px;
    top: 45px;
    display: none;
    cursor: pointer;
}

.toggle-button span {
    display: inline-block;
    width: 100%;
    height: 2px;
    background-color: white;
    float: left;
    margin-bottom: 8px;
}

.bookatable {
    color: #fff;
    background-color: #555556;
    border-radius: 6px;
    text-transform: uppercase;
    font-weight: 600;
    font-size: 18px;
    line-height: 1;
    text-align: center;
    padding: 9px 6px 8px 8px;
    transition-duration: 0.6s;
    transition-timing-function: ease-in-out;
    letter-spacing: -.3px;
    cursor: pointer;
}

.bookatable:hover {
    cursor: pointer;
    background-color: #909092;
    color: white;
}





/* ---- BREAKPOINTS ---- */

@media (max-width: 1100px) {

    header {
        display: flex;
        flex-direction: column;
        text-align: center;
        position: relative;
        justify-content: space-between;
        padding: 5px 20px 5px;
    }

    .logo {
        align-self: flex-start;
    }
    
    .toggle-button{
        display: block;
    }
    
    nav{
        display: none;
        width: 100%;
        border-top: 1px solid white;
        padding-top: 20px 0;
        margin-top: 30px;
    }

    nav ul li{
        padding: 15px 0px;
        width: 100%;
    }

    nav ul {
        text-align: center;
    }

    nav.show{
        display: flex;
        flex-direction: column;
        flex-wrap: nowrap;
    }

    .bookatable {
        display: none;
    }

    .bookatabledd {
        display: block;
    }
}

enter image description here

Solution

You CSS file contains:

nav ul li{
    padding: 15px 0px;
    width: 100%;
}

Which means that even the element containing the 'Book a table' item has its padding which takes up space in the navbar even when its child element is not displayed.

Here's the correct code:

li#hidden {
  padding: 0;
}

// Make sure you give it padding when the page is below 1100px wide

@media (max-width: 1100px) {
 // ...
 li#hidden {
    padding: 15px;
  }
}

<nav id="nav">
                <ul>
                    <li><a href="#">Home</a></li>
                    <li><a href="#">Menu</a></li>
                    <li><a href="#">About Us</a></li>
                    <li><a href="#">Contact Us</a></li>
                    <!-- The item below must not have padding -->
                    <li id ="hidden"><a href="#" class="bookatabledd">Book A Table</a></li>
                </ul>
            </nav>