HTML

center iframe

<div class="iframe-container">
  <!--iframe link is the link to the jsfiddle-->
  <iframe src="https://jsfiddle.net/8z9s1t6x/2/"></iframe>
</div>

<style>
  .iframe-container {
		text-align:center;
  		width:100%;
  }
</style>

center iframe in editor

/* center iframe in editor */
/* div wrapping ifrrame */
div {
    display: flex;
    align-items: center;
    justify-content: center;
}

iframe center

<div style="text-align:center;"><iframe style="
display:auto;
width="560" height="315" src="https://www.youtube.com/embed/" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe></div>

Center an iframe

div, iframe {
    width: 100px;
    height: 50px;
    margin: 0 auto;
    background-color: #777;
}

iframe {
    display: block;
    border-style:none;
}