The Expand Gallery button is not showing as your gallery is being loaded into an iframe (and if the gallery was expanded, it would fill only the iframe rather than the parent page).

Unfortunately, there are certain drawbacks to using an iframe (they are listed on this web page, scroll down to "2) Using an iframe") and one of them is that the Expand Gallery button is disabled.

Embed your gallery directly into your web page (following the embedding instructions here) and the Expand Gallery button will display and function as expected.

Unfortunately, Blogger is not a regular web host (with FTP access to the web space that they provide) so you'll probably need to use an iframe (with its limitations) in this situation (following the Embedding in a Web Template Site instructions).

All Juicebox gallery files should be on the same domain (or subdomain) as the web page which contains the gallery's JavaScript embedding code due to the same-origin policy.
Please see here for details: https://developer.mozilla.org/en-US/doc … gin_policy

In order to use files on a different domain, you could implement a Cross-Origin Resource Sharing (CORS) solution. More information about CORS can be found here: https://www.w3.org/TR/cors/

If your gallery is hosted on an Apache server, then add the following line of code to the .htaccess file in the root directory of the domain which hosts the gallery folder.

Header add Access-Control-Allow-Origin "*"

If you use an IIS server, then please see this link for a similar solution: https://enable-cors.org/server_iis7.html

I hope this helps (otherwise you might need to continue using an iframe for your Blogger site).