On display setting the first accordion is change background, from here you can set the background of popup or if you want to apply a static color then you can choose the color from color picker.
You can see set on background radio options from, here you can choose that
In second accordion there are options available for edit button style.
From here you can set button text, background color, font style, position, and link.
In Third Accordion you can set entrance and exit animation effect.
In the last accordion, you can insert custom CSS, from here you can enter your custom CSS if you want.
After done all change please save it.