center megamenu div under nav button

I have used some code which I got from W3 schools to create a megamenu. I want the box to appear centred to the nav button selected, not centred to the whole page. I’m not really concerned about the mini view, it is full screen mode I am trying to set up. Everything else works fine apart from the alignment issue. My full code is here without the header code.

function myFunction() {
    var x = document.getElementById("myTopnav");
    if (x.className === "navbar") {
        x.className += " responsive";
    } else {
        x.className = "navbar";
    }
}
* {
    box-sizing: border-box;
}

body {
    margin: 0;
}

.navbar {
    overflow: hidden;
    background-color: #333;
    border-radius: 5px;
}

.navbar a {
    float: left;
    font-size: 16px;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
}

.navbar .icon {
    display: none;
}

.dropdown {
    float: left;
    overflow: hidden;
}

.dropdown .dropbtn {
    font-size: 16px;
    border: none;
    outline: none;
    color: white;
    padding: 14px 16px;
    background-color: inherit;
    font: inherit;
    margin: 0;
}

.dropdown-content {
    display: none;
    position: absolute;
    background-color: #f9f9f9;
    width: 60%;
    left: 0;
    box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
    z-index: 1;
    border-radius: 10px;
}

.navbar .dropdown>.dropdown-content {
    left: 50%;
    transform: translate3d(-50%, 10px, 0);
}

.dropdown-content a {
    float: none;
    color: black;
    padding: 12px 16px;
    text-decoration: none;
    display: block;
    text-align: left;
}

.navbar a:hover,
.dropdown:hover .dropbtn {
    background-color: #555;
    color: white;
}

.dropdown-content a:hover {
    background-color: #ddd;
    color: black;
}

.dropdown:hover .dropdown-content {
    display: block;
}

@media screen and (max-width: 992px) {
    .navbar a:not(:first-child),
    .dropdown .dropbtn {
        display: none;
    }

    .navbar a.icon {
        float: right;
        display: block;
    }
}

/* Create three equal columns that floats next to each other */
.column {
    float: left;
    width: 33.33%;
    padding: 10px;
    background-color: #fff;
    height: 250px;
    border-radius: 10px;
}

.column a {
    float: none;
    color: black;
    padding: 16px;
    text-decoration: none;
    display: block;
    text-align: left;
}

.column a:hover {
    background-color: #eff;
}

/* Clear floats after the columns */
.row:after {
    content: "";
    display: table;
    clear: both;
}

@media screen and (max-width: 992px) {
    .navbar.responsive {
        position: relative;
    }

    .navbar.responsive .icon {
        position: absolute;
        right: 0;
        top: 0;
    }

    .navbar.responsive a {
        float: none;
        display: block;
        text-align: left;
    }

    .navbar.responsive .dropdown {
        float: none;
    }

    .navbar.responsive .dropdown-content {
        position: relative;
    }

    .navbar.responsive .dropdown .dropbtn {
        display: block;
        width: 100%;
        text-align: left;
    }

    .column {
        width: 100%;
        height: auto;
    }
}
<div class="line">
    <div class="s-12 l-12 center">
        <div class="navbar margin-bottom" id="myTopnav">
            <a href="#home">Home</a>
            <a href="#news">News</a>
            <a href="#news">News</a>
            <a href="#news">News</a>
            <a href="#news">News</a>
            <div class="dropdown">
                <button class="dropbtn">Dropdown <i class="fa fa-caret-down"></i>
                </button>
                <div class="dropdown-content">
                    <div class="row">
                        <div class="column">
                            <h3>Category 1</h3>
                            <a href="#">Link 1</a>
                            <a href="#">Link 2</a>
                            <a href="#">Link 3</a>
                        </div>
                        <div class="column">
                            <h3>Category 2</h3>
                            <a href="#">Link 1</a>
                            <a href="#">Link 2</a>
                            <a href="#">Link 3</a>
                        </div>
                        <div class="column">
                            <h3>Category 3</h3>
                            <a href="#">Link 1</a>
                            <a href="#">Link 2</a>
                            <a href="#">Link 3</a>
                        </div>
                    </div>
                </div>
            </div>
            <a href="#news">News</a>
            <a href="#news">News</a>
            <div class="dropdown">
                <button class="dropbtn">Dropdown <i class="fa fa-caret-down"></i>
                </button>
                <div class="dropdown-content">
                    <div class="row">
                        <div class="column">
                            <h3>Category 1</h3>
                            <a href="#">Link 1</a>
                            <a href="#">Link 2</a>
                            <a href="#">Link 3</a>
                        </div>
                        <div class="column">
                            <h3>Category 2</h3>
                            <a href="#">Link 1</a>
                            <a href="#">Link 2</a>
                            <a href="#">Link 3</a>
                        </div>
                        <div class="column">
                            <h3>Category 3</h3>
                            <a href="#">Link 1</a>
                            <a href="#">Link 2</a>
                            <a href="#">Link 3</a>
                        </div>
                    </div>
                </div>
            </div>
            <a href="javascript:void(0);" class="icon" onclick="myFunction()">
                <i class="fa fa-bars"></i>
            </a>
        </div>
    </div>
</div>

I have tried targeting the .dropdown-content class mostly. It always seems to break the navbar which inserts the dropdown box inside the navbar instead of below the navbar.