om.Campaign.afterShow

document.addEventListener('om.Campaign.afterShow', function(event) {

    if (event.detail.Campaign.id == 'zjd3hxxogbfvmy2iz0rp') // your slug

    {

        var campaignID = 'om-'+ event.detail.Campaign.id;

        var campaignHeight = document.getElementById(campaignID).offsetHeight;

        var fixedElement = document.getElementById('top'); //give ID for your fixed element OR document.querySelector('.yourClassName.yourSecondClassName');

        fixedElement.style.top = campaignHeight + 'px';

    }

});

document.addEventListener('om.Campaign.close', function(event) {

    var fixedElement = document.getElementById('top'); //give ID for your fixed element or document.querySelector('.yourClassName.yourSecondClassName');

    fixedElement.style.top = 0;

});