You can customize the Close Button of the “Popup” block using the Combo Blocks plugin. This article will help you to customize the Popup close button.
To begin, insert a “Popup” block.
Click on the “Close” tab.
Here you can choose the icon of the Close Button.
Then, choose a Popup Close Animation.
Now, click on the Styles Tab and add some styles. If you don’t know how to style an element, then read this document.