Currently there’s no way to add custom CSS to popups (both the popup widget and the poupup in the portfolio widget). It would be awesome to be able to apply custom css there)
Great news — Custom CSS is now available for Popup! 🎉
See where you will find this option:
Go to your widget Settings tab
Find Custom CSS field and add any code you need
Feel welcome to check the widget out in our Popup online demo!
And we'll be happy to hear your feedback in the comments below 🙂