Which app do you mean exactly (it is always handy to provide the link to the appstore content so there is no confusion about which app we talking about)? If you are talking about the mobile slider widget there is a tutorial about that one: https://world.mendix.com/display/howto50/The+Mobile+Slider+Custom+Widget
Regards,
Ronald [EDIT]
There was a forum post about those panels: https://community.mendix.com/questions/7528/Availablity-widget-used-in-Mendix-Appstore It's just done with css.