How to Style Iframe Content from Another Domain with CSS

How to Style Iframe Content from Another Domain with CSS

Styling an iframe that contains content from another domain can be challenging due to security restrictions imposed by web browsers. However, there are ways to overcome these restrictions and apply custom styles to the iframe content.

One approach is to use the postMessage() method, which allows communication between the parent window and the iframe. Using this method, you can send CSS styles from the parent window to the iframe and apply them to the iframe’s content.

Here’s an example of how to use postMessage() to apply styles to an iframe:

In the parent window:

const iframe = document.querySelector('iframe');
const styles = `
  body {
    font-family: Arial, sans-serif;
    background-color: #f2f2f2;
  }
`;
iframe.contentWindow.postMessage(styles, '*');

In the iframe:

<html>
  <head>
    <script>
      window.addEventListener('message', event => {
        if (event.origin !== 'https://www.parentdomain.com') return;
        const style = document.createElement('style');
        style.textContent = event.data;
        document.head.appendChild(style);
      });
    </script>
  </head>
  <body>
    <!-- iframe content -->
  </body>
</html>

In this example, the parent window sends the CSS styles as a string to the iframe using postMessage(). The iframe listens for the message using the window.addEventListener() method, checks that it’s coming from an allowed origin, creates a style element, and appends it to the head of the iframe’s document.

It’s important to note that this method requires cooperation between the parent window and the iframe’s content, and it may not work if the content in the iframe is not designed to accept custom styles.

In summary, using the postMessage() method to apply styles to an iframe’s content from another domain can be done by sending the CSS styles as a string from the parent window to the iframe and then applying them to the iframe’s document. While it’s not a foolproof solution, it can be a useful technique when styling an iframe that contains content from another domain.

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