Describe the bug
The preview feature for newsletters in the admin panel displays content within a significantly reduced layout size, making it impossible to view the entire newsletter content without scrolling.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://nightly.decidim.org/ and log in to the admin panel.
2. Navigate to 'Newsletters' and create a new one.
3. Click on the 'Preview' button to review the newsletter's appearance before sending.
4. See the constrained size of the preview window, necessitating excessive scrolling to view all content.

Expected behavior
The newsletter preview should present the whole content in a layout that allows administrators to easily review the entire newsletter without the need to scroll.

Screenshots

Extra data (please complete the following information):

• Device: Desktop
• Device OS: Ubuntu 22.04
• Browser: Chrome
• Decidim Version: 0.29.0.dev
• Decidim installation: Nightly