The .collapse class indicates a collapsible element (a <div> in our example);
this is the content that will be shown or hidden with a click of a button.
To control (show/hide) the collapsible content, add the data-toggle="collapse" attribute to an <a> or a <button> element.
Then add the data-target="#id" attribute to
connect the button with the collapsible content (<div id="demo">).
The following example shows a collapsible panel:
The following shows a collapsible panel with a list group inside: