Extract number from txt file and use as jquery variable to incrementally increase circle

Question

I need a circle to grow every time a button is cumulatively clicked, which means it needs to be server stored and not locally stored. As of now, I have managed to count the clicks via this php code, which stores in a .txt file the amount of times the button has been clicked:

<?php

if( isset($_POST['clicks']) ) { 
    incrementClickCount();
}

function getClickCount()
{
    return (int)file_get_contents("clickit.txt");
}

function incrementClickCount()
{
    $count = getClickCount() + 1;
    file_put_contents("clickit.txt", $count);
}

?>

I would like to extract the number in the clickit.txt and use it to increment, with jquery, the size of a circle via css.

var numberClicks = ${'#number-clicks', 'value'}

$('.main-circle').css('width', 'numberClicks', 'vw')

.main-circle {
    position: fixed;
    width: 1vw;
    height: 1vw;
    top: 50%;
    bottom: 50%;
    left: 50%;
    border-radius: 50%;
    background-color: yellow;
    transform: translate(-50%, -50%);

}

<div class="main-circle"></div>

<form action="<?php $_SERVER['PHP_SELF']; ?>" method="post">
    <input type="submit" value="neuer erfolg" name="clicks">
    </form>
    <div>Click Count: <span id="number-clicks"<?php echo getClickCount(); ?> </div>

I know this doesn't work as is, but I can't figure out the correct syntax. Any help is much appreciated!