In odoo official site's blog section there is a nice effect. In the blogpost, there is a link to another blogpost at the bottom. If you click on the read more button the background gets bigger and automatically loads the content of that blog post. 

Example can be found here: https://www.odoo.com/blog/odoo-news-5/post/odoo-10-released-337

Can anyone tell me how can I achieve this effect?