How to center an iframe horizontally?

Question

Add display:block; to your iframe css.

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

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

<div>div</div>
<iframe src="data:,iframe"></iframe>

best way and more simple to center an iframe on your webpage is :

<p align="center"><iframe src="http://www.google.com/" width=500 height="500"></iframe></p>

where width and height will be the size of your iframe in your html page.

HTML:

<div id="all">
    <div class="sub">div</div>
    <iframe>ss</iframe>
</div>

CSS:

#all{
    width:100%;
    float:left;
    text-align:center;
}
div.sub, iframe {
    width: 100px;
    height: 50px;
    margin: 0 auto;
    background-color: #777;

}

The simplest code to align the iframe element:

<div align="center"><iframe width="560" height="315" src="www.youtube.com" frameborder="1px"></iframe></div>

If you are putting a video in the iframe and you want your layout to be fluid, you should look at this webpage: Fluid Width Video

Depending on the video source and if you want to have old videos become responsive your tactics will need to change.

If this is your first video, here is a simple solution:

<div class="videoWrapper">
    <!-- Copy & Pasted from YouTube -->
    <iframe width="560" height="349" src="http://www.youtube.com/embed/n_dZNLr2cME?rel=0&hd=1" frameborder="0" allowfullscreen></iframe>
</div>

And add this css:

.videoWrapper {
	position: relative;
	padding-bottom: 56.25%; /* 16:9 */
	padding-top: 25px;
	height: 0;
}
.videoWrapper iframe {
	position: absolute;
	top: 0;
	left: 0;
	width: 100%;
	height: 100%;
}

Disclaimer: none of this is my code, but I've tested it and was happy with the results.