For a Wordpress-Site I want to use the collapse-function of bootstrap. If you watch the website with a smartphone or tablet, you don't see the whole content. Like Wikipedia.

On a desktop it is default to see the content.

I can't duplicate the content and just use the bootstrap classes visible-xs and hidden-xs, because it is a side for a client, and I can't double content.

How can I say that the default on mobile is .collapse and the default on desktop is .collapse.in ?

Thanks a lot!