pop up window

Hello guys,

here (https://www.giraffe.net/classic/menu/breakfast)you can see a menu page and under each menu there are some symbol like this: “i”(in a circle). If you go there with the cursor a popup window will appear showing details about ingredients Allergy . I would like to put something like that in my web page.
Can you suggest va plug in or I ave to manage the CSS edit page?
That is the page where I wont to do this: https://homecookingse24.co.uk/our-menu/

thanks