change the z-index of iframe
// responsivity
// and modify the z-index of the iframe
<style>
.publicity{
position: relative;
overflow: hidden;
text-align: center;
margin-top: 20px;
padding-top: 56.25%;
z-index:-1;
}
.publicity iframe {
position: absolute;
top: 0;
left: 0;
bottom: 0;
right: 0;
width: 100%;
height: 100%;
z-index:auto;
}
</style>
<body>
<div class="publicity">
<iframe width="560" height="315"
src="https://www.youtube.com/embed/zGrYiMaAlJs?loop=1&muted=1"
title="YouTube video player"
frameborder="0"
allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
allowfullscreen></iframe>
</div>
</body>