A CSS pseudo-element is used to style specified parts of an element. This portion of element is not identified as a separate element in the DOM. However, it may have its own event handling on clicks etc. Since it is not a separate element in the DOM, you may not be able to save this as an element in the element explorer.
To handle clicks on such pseudo elements (marked with yellow boundary above), hover on the full element (marked in red boundary above) and select command, "Click Coordinates". This command performs a click at given x, y position on an element, relative to a given corner.
Click Coordinates Clicks an element at a give position. X and Y coordinates are specified relative to the element itself.
In this case, you will choose "bottom-right" corner and provide, may be 10 px for x and 10 px for y coordinate. This will cause button click at a position slightly above and to the left of the lower right corner.