how to position my dropdown just under the top bar

function TrainDropdown() { 
  const trainMenu = document.getElementById("trains");
  trainMenu.classList.toggle("show");
  console.log("TrainDropdown toggled:", trainMenu.classList.contains("show"));
}

  function Menu() {
    const navBar = document.getElementById("phone-nav-bar");
    navBar.classList.toggle("show-nav-bar");
}
function MobileTrainDropdown() {
  const trainElements = document.getElementById("tablet-trains");
  if (trainElements.style.display === "none") {
      trainElements.style.display = "flex";
  } else {
      trainElements.style.display = "none";
  }
}

window.addEventListener("click", function (event) {
  console.log("Window click detected on:", event.target);

  // Close train dropdown if clicked outside the dropdown button
  if (!event.target.closest('.dropdown-button')) {
    const dropdowns = document.getElementsByClassName("train-elements");
    for (let i = 0; i < dropdowns.length; i++) {
      const openDropdown = dropdowns[i];
      if (openDropdown.classList.contains('show')) {
        openDropdown.classList.remove('show');
        console.log("Closed train dropdown:", openDropdown);
      }
    }
  }

  // Close mobile nav menu if clicked outside menu button and nav bar
  const navBar = document.getElementById("phone-nav-bar");
  const menuButton = document.querySelector('.menu-button');
  if (navBar && menuButton && !menuButton.contains(event.target) && !navBar.contains(event.target)) {
    navBar.classList.remove("show-nav-bar");
    console.log("Closed mobile nav menu.");
  }
});

body {
    margin: 0;
}

/*top-bar properties*/
.top-bar {
    display: flex;
    align-items: center;
    height: 10vh;
    background-color: #A7C4FF;
}

.branding {
    display: flex;
    align-items: center;
}

.branding img {
    height: 12vh; /* Set a fixed height for the logo */
    width: auto; /* Maintain aspect ratio */
}

/*menu toggle properties*/
.menu-button {
    display: none; /* Hidden on larger screens */
}

.mobile-phone-nav-bar {
    position: absolute; /* Position below the top bar */
    top: 10vh; /* Position below the top bar */
    left: 0; /* Align to the left */
    width: 100%; /* Full width */
    display: none; /* Hidden by default */
}

.mobile-phone-branding {
    display: none; /* Hidden on larger screens */
}
/*navigation bar properties*/
.nav-bar {
    display: flex;
    flex: 1;
    align-items: center;
    margin-left: 10vw;
}

/*buttons*/
.nav-button, .dropdown-button{
    width: 100%;
    height: 8vh;
    line-height: 8vh;
    margin-right: 5px;
    font-family: Unbounded;   
    font-size: 1vw; 
    text-align: center;
    text-decoration: none;
    background-color: #A7C4FF;
    border: none;
    border-radius: 40px;
    transition: background-color 0.4s ease-in-out;
}

.nav-button:hover, .dropdown-button:hover{
    background-color: #8FA9FF;
}

/*train-dropdown and all its children properties*/
.train-dropdown{
    position: relative;
    margin-right: 5px;
    width: 100%;
}

.train-elements{
    display: none;
    width: 100%;
    position: absolute;
    top: 10vh;
    background-color: #7f9dfd;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
    border-radius: 0.8vw;
    z-index: 1;
}

.train-elements a{
    padding: 1em;
    color: black;
    text-decoration: none;
}

.train-elements a:hover{
    background-color: #567dff;
}

.train-elements #first-element:hover{
    border-top-left-radius: 0.8vw;
    border-top-right-radius: 0.8vw;
}

.train-elements #last-element:hover{
    border-bottom-left-radius: 0.8vw;
    border-bottom-right-radius: 0.8vw;
}

#mobile-phone-train-button{
    display: none;
}

/*Class that JS uses to show train-elements*/
.show{
    display: flex;
    flex-direction: column;
}

@media only screen and (max-width: 1300px){
    /*hiding nav-bar to save space and make it into a dropdown*/
    .nav-bar{
        display: none;
    }

    /*a menu button that makes the nav-bar appear*/
    .menu-toggle{
        position: relative;
    }

    .menu-button{
        display: flex;
        height: 8.5vh;
        width: 8.5vh;
        justify-content: center;
        align-items: center;
        margin: 10px;
        border-radius: 20px;
        border: none;
        background-color: #A7C4FF;
    }

    .menu-button img {
        width: 5vw; /* Set a fixed width */
        height: auto; /* Maintain aspect ratio */
        max-width: none; /* Prevent scaling */
    }

    .menu-button:hover{
        background-color: #8FA9FF;
    }

    /*button properties*/
    .nav-button, .dropdown-button{
        border-radius: 0;
        background-color: #94b7ff;
    }

    .mobile-phone-nav-bar{
        position: absolute;
        box-shadow: 8px 16px 16px 0px rgba(0,0,0,0.2);
        background-color: #A7C4FF;
        width: 300px;
        top: 10vh;
    }
    
    /*train dropdown properties*/
    .tablet-train-elements{
        display: none;
        width: 100%;
        flex-direction: column;
        position: absolute;
        background-color: #7f9dfd;
    }
    
    .tablet-train-elements a{
        padding: 12px 16px;
        color: black;
        text-decoration: none;
    }

    .tablet-train-elements a:hover{
        background-color: #567dff;
    }
    
    /*hides the button i will be using for phone mode that
    substitutes the dropdown button cause there is no space*/
    #mobile-phone-train-button{
        display: none;
    }

    /*a class JS uses to display the dropdown when pressing the button*/
    .show-nav-bar{
        display: flex;
        flex-direction: column;
    }
}

<!DOCTYPE html>
<html lang="bg">
<head>
    
    <!--meta data-->
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <!--tab view-->
    <title>Железопътна страст</title>
    <link rel="icon" href="assets/images/favicon.png">

    <!--css files-->
    <link rel="stylesheet" href="assets/css/index.css">
    <link rel="stylesheet" href="topbar/topbar.css">

    <!--google fonts-->
    <link rel="preconnect" href="https://fonts.googleapis.com">
    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
    <link href="https://fonts.googleapis.com/css2?family=Unbounded:[email protected]&display=swap" rel="stylesheet">

</head>
<script src="topbar/topbar.js" defer></script>
<body>    
    <!--the top bar-->
    <div class="top-bar">
        <div class="mobile-phone-branding">

            <a href="index.html"><img id="logo" src="assets/images/logo.png" alt="Лого на влак"></a>

        </div>
        <div class="menu-toggle">

            <button class="menu-button" onclick="Menu()"><img src="assets/images/menu.png"></button>
            
            <div class="mobile-phone-nav-bar" id="phone-nav-bar">

                <a class="nav-button" href="index.html">Начало</a>

                <a class="nav-button" id="mobile-phone-train-button" href="#trains">Влакове</a>
                
                <div class="tablet-train-dropdown">
                    
                    <button onclick="MobileTrainDropdown()" class="dropdown-button">Влакове</button>
                    
                    <div id="tablet-trains" class="tablet-train-elements">
                    
                        <a href="#">Link 1</a>
                        
                        <a href="#">Link 2</a>
    
                        <a href="#">Link 3</a>
                    
                    </div>

                </div> 
                
                <a class="nav-button" href="#contacts">Контакти</a>
                <a class="nav-button" href="#aboutme">Повече за мен</a>
            
            </div>

        </div>
        
        <div class="branding">

            <a href="index.html"><img id="logo" src="assets/images/logo.png" alt="Лого на влак"></a>

        </div>
        
        <div class="nav-bar">

            <a class="nav-button" href="index.html">Начало</a>
            
            <div class="train-dropdown">
                
                <button onclick="TrainDropdown()" class="dropdown-button">Влакове</button>
                
                <div id="trains" class="train-elements">
                
                    <a id="first-element" href="#">Link 1</a>
                    
                    <a href="#">Link 2</a>

                    <a id="last-element" href="#">Link 3</a>
                
                </div>

            </div> 
            
            <a class="nav-button" href="#contacts">Контакти</a>
            <a class="nav-button" href="#aboutme">Повече за мен</a>
        
        </div>

    </div>   

   
</body>
</html>