How to apply CSS to iframe?

Question

Edit: This does not work cross domain unless the appropriate CORS header is set.

There are two different things here: the style of the iframe block and the style of the page embedded in the iframe. You can set the style of the iframe block the usual way:

<iframe name="iframe1" id="iframe1" src="empty.htm" 
        frameborder="0" border="0" cellspacing="0"
        style="border-style: none;width: 100%; height: 120px;"></iframe>

The style of the page embedded in the iframe must be either set by including it in the child page:

<link type="text/css" rel="Stylesheet" href="Style/simple.css" />

Or it can be loaded from the parent page with Javascript:

var cssLink = document.createElement("link");
cssLink.href = "style.css"; 
cssLink.rel = "stylesheet"; 
cssLink.type = "text/css"; 
frames['iframe1'].document.head.appendChild(cssLink);

I met this issue with Google Calendar. I wanted to style it on a darker background and change font.

Luckily, the URL from the embed code had no restriction on direct access, so by using PHP function file_get_contents it is possible to get the entire content from the page. Instead of calling the Google URL, it is possible to call a php file located on your server, ex. google.php, which will contain the original content with modifications:

$content = file_get_contents('https://www.google.com/calendar/embed?src=%23contacts%40group.v.calendar.google.com&ctz=America/Montreal');

Adding the path to your stylesheet:

$content = str_replace('</head>','<link rel="stylesheet" href="http://www.yourwebsiteurl.com/google.css" /></head>', $content);

(This will place your stylesheet last just before the head end tag.)

Specify the base url form the original url in case css and js are called relatively:

$content = str_replace('</title>','</title><base href="https://www.google.com/calendar/" />', $content);

The final google.php file should look like this:

<?php
$content = file_get_contents('https://www.google.com/calendar/embed?src=%23contacts%40group.v.calendar.google.com&ctz=America/Montreal');
$content = str_replace('</title>','</title><base href="https://www.google.com/calendar/" />', $content);
$content = str_replace('</head>','<link rel="stylesheet" href="http://www.yourwebsiteurl.com/google.css" /></head>', $content);
echo $content;

Then you change the iframe embed code to:

<iframe src="http://www.yourwebsiteurl.com/google.php" style="border: 0" width="800" height="600" frameborder="0" scrolling="no"></iframe>

Good luck!

If the content of the iframe is not completely under your control or you want to access the content from different pages with different styles you could try manipulating it using JavaScript.

var frm = frames['frame'].document;
var otherhead = frm.getElementsByTagName("head")[0];
var link = frm.createElement("link");
link.setAttribute("rel", "stylesheet");
link.setAttribute("type", "text/css");
link.setAttribute("href", "style.css");
otherhead.appendChild(link);

Note that depending on what browser you use this might only work on pages served from the same domain.

var $head = $("#eFormIFrame").contents().find("head");

$head.append($("<link/>", {
    rel: "stylesheet",
    href: url,
    type: "text/css"
}));

Here is how to apply CSS code directly without using <link> to load an extra stylesheet.

var head = jQuery("#iframe").contents().find("head");
var css = '<style type="text/css">' +
          '#banner{display:none}; ' +
          '</style>';
jQuery(head).append(css);

This hides the banner in the iframe page. Thank you for your suggestions!

If you control the page in the iframe, as hangy said, the easiest approach is to create a shared CSS file with common styles, then just link to it from your html pages.

Otherwise it is unlikely you will be able to dynamically change the style of a page from an external page in your iframe. This is because browsers have tightened the security on cross frame dom scripting due to possible misuse for spoofing and other hacks.

This tutorial may provide you with more information on scripting iframes in general. About cross frame scripting explains the security restrictions from the IE perspective.